Method and apparatus for decoding video, and method and apparatus for encoding video

ABSTRACT

Provided are a video decoding method and apparatus for, in a video encoding and decoding procedure, when a merge candidate list of a current block is configured, determining whether the number of merge candidates included in the merge candidate list is greater than 1 and is smaller than a predetermined maximum merge candidate number, when the number of the merge candidates included in the merge candidate list is greater than 1 and is smaller than the predetermined maximum merge candidate number, determining an additional merge candidate by using a first merge candidate and a second merge candidate of the merge candidate list of the current block, configuring the merge candidate list by adding the determined additional merge candidate to the merge candidate list, and performing prediction on the current block, based on the merge candidate list.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 17/417,009 filedJun. 21, 2021, which is a National Stage of International ApplicationNo. PCT/KR2019/018222 filed Dec. 20, 2019, which claims benefit of U.S.Provisional No. 62/792,233 filed on Jan. 14, 2019 and which claimsbenefit of U.S. Provisional No. 62/783,665 filed Dec. 21, 2018 in theUnited States Patent and Trademark Office. The disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The disclosure relates to a video decoding method and a video decodingapparatus, and more particularly, to an image encoding method andapparatus and an image decoding method and apparatus, in which, when amerge candidate list of a current block is configured, it is determinedwhether the number of merge candidates included in the merge candidatelist is greater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, an additional mergecandidate is obtained by using a first merge candidate and a secondmerge candidate of the merge candidate list of the current block, theobtained additional merge candidate is added to the merge candidate listto update the merge candidate list, and prediction is performed on thecurrent block, based on the merge candidate list.

BACKGROUND ART

Image data is encoded by a codec according to a predetermined datacompression standard, for example, a moving picture expert group (MPEG)standard, and then is stored in the form of a bitstream in a recordingmedium or is transmitted via a communication channel.

With the development and supply of hardware capable of reproducing andstoring high-resolution or high-definition image content, there is anincreasing demand for a codec for effectively encoding or decoding thehigh-resolution or high-definition image content. Encoded image contentmay be reproduced by being decoded. Recently, methods for effectivelycompressing such high-resolution or high-definition image content areperformed. For example, the methods are proposed to effectivelyimplement an image compression technology through a process of splittingan image to be encoded by a random method or rendering data.

As one of techniques for rendering data, it is general that, when aprediction mode is a merge mode, a spatial candidate being spatiallyadjacent to a current block, a temporal candidate being temporallyadjacent to the current block, and a zero motion vector candidate areincluded in a merge candidate list.

DESCRIPTION OF EMBODIMENTS Technical Problem

In a video encoding and decoding procedure, proposed are a method andapparatus for, when a merge candidate list of a current block isconfigured, determining whether the number of merge candidates includedin the merge candidate list is greater than 1 and is smaller than apredetermined maximum merge candidate number, when the number of themerge candidates included in the merge candidate list is greater than 1and is smaller than the predetermined maximum merge candidate number,obtaining an additional merge candidate by using a first merge candidateand a second merge candidate of the merge candidate list of the currentblock, adding the obtained additional merge candidate to the mergecandidate list to update the merge candidate list, and performingprediction on the current block, based on the merge candidate list.

Solution to Problem

To solve the technical problem, the disclosure may provide a videodecoding method including: when a merge candidate list of a currentblock is configured, determining whether the number of merge candidatesincluded in the merge candidate list is greater than 1 and is smallerthan a predetermined maximum merge candidate number; when the number ofthe merge candidates included in the merge candidate list is greaterthan 1 and is smaller than the predetermined maximum merge candidatenumber, obtaining an additional merge candidate by using a first mergecandidate and a second merge candidate of the merge candidate list ofthe current block; updating the merge candidate list by adding theobtained additional merge candidate to the merge candidate list; andperforming prediction on the current block, based on the merge candidatelist.

To solve the technical problem, the disclosure may provide a videodecoding apparatus including: a memory; and at least one processorconnected to the memory, wherein the at least one processor isconfigured to, when a merge candidate list of a current block isconfigured, determine whether the number of merge candidates included inthe merge candidate list is greater than 1 and is smaller than apredetermined maximum merge candidate number, when the number of themerge candidates included in the merge candidate list is greater than 1and is smaller than the predetermined maximum merge candidate number,obtain an additional merge candidate by using a first merge candidateand a second merge candidate of the merge candidate list of the currentblock, update the merge candidate list by adding the obtained additionalmerge candidate to the merge candidate list, and perform prediction onthe current block, based on the merge candidate list.

To solve the technical problem, the disclosure may provide a videoencoding method including: when a merge candidate list of a currentblock is configured, determining whether the number of merge candidatesincluded in the merge candidate list is greater than 1 and is smallerthan a predetermined maximum merge candidate number; when the number ofthe merge candidates included in the merge candidate list is greaterthan 1 and is smaller than the predetermined maximum merge candidatenumber, obtaining an additional merge candidate by using a first mergecandidate and a second merge candidate of the merge candidate list ofthe current block; updating the merge candidate list by adding theobtained additional merge candidate to the merge candidate list; andperforming prediction on the current block, based on the merge candidatelist.

To solve the technical problem, the disclosure may provide a videoencoding apparatus including a memory; and at least one processorconnected to the memory, wherein the at least one processor isconfigured to, when a merge candidate list of a current block isconfigured, determine whether the number of merge candidates included inthe merge candidate list is greater than 1 and is smaller than apredetermined maximum merge candidate number, when the number of themerge candidates included in the merge candidate list is greater than 1and is smaller than the predetermined maximum merge candidate number,obtainan additional merge candidate by using a first merge candidate anda second merge candidate of the merge candidate list of the currentblock, update the merge candidate list by adding the obtained additionalmerge candidate to the merge candidate list, and perform prediction onthe current block, based on the merge candidate list.

Advantageous Effects of Disclosure

In a video encoding and decoding procedure, when a merge candidate listof a current block is configured, it is determined whether the number ofmerge candidates included in the merge candidate list is greater than 1and is smaller than a predetermined maximum merge candidate number, whenthe number of the merge candidates included in the merge candidate listis greater than 1 and is smaller than the predetermined maximum mergecandidate number, an additional merge candidate is obtained by using afirst merge candidate and a second merge candidate of the mergecandidate list of the current block, the obtained additional mergecandidate is added to the merge candidate list to update the mergecandidate list, and prediction is performed on the current block, basedon the merge candidate list, such that the prediction with respect tothe current block may be efficiently improved. That is, when aparticular condition is satisfied, one additional candidate may bedetermined by using a first candidate and a second candidate of a mergecandidate list, and the determined additional candidate may be added tothe merge candidate list, so that the merge candidate list may berapidly and efficiently configured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a schematic block diagram of an image decodingapparatus according to an embodiment.

FIG. 2 illustrates a flowchart of an image decoding method according toan embodiment.

FIG. 3 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a current codingunit, according to an embodiment.

FIG. 4 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a non-square codingunit, according to an embodiment.

FIG. 5 illustrates a process, performed by an image decoding apparatus,of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

FIG. 6 illustrates a method, performed by an image decoding apparatus,of determining a predetermined coding unit from among an odd number ofcoding units, according to an embodiment.

FIG. 7 illustrates an order of processing a plurality of coding unitswhen an image decoding apparatus determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

FIG. 8 illustrates a process, performed by an image decoding apparatus,of determining that a current coding unit is to be split into an oddnumber of coding units, when the coding units are not processable in apredetermined order, according to an embodiment.

FIG. 9 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a first codingunit, according to an embodiment.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined when an image decoding apparatus splits afirst coding unit, satisfies a predetermined condition, according to anembodiment.

FIG. 11 illustrates a process, performed by an image decoding apparatus,of splitting a square coding unit when split shape mode informationindicates that the square coding unit is to not be split into foursquare coding units, according to an embodiment.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of predetermined data units included in a picture,according to an embodiment.

FIG. 16 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture,according to an embodiment.

FIG. 17 is a block diagram of a video encoding apparatus according to anembodiment.

FIG. 18 is a flowchart illustrating a video encoding method according toan embodiment.

FIG. 19 illustrates a block diagram of the video decoding apparatusaccording to an embodiment.

FIG. 20 illustrates a flowchart of the video decoding method accordingto an embodiment.

FIG. 21 is a diagram for describing a procedure in which a mergecandidate list of a current block is configured.

FIG. 22 is a diagram for describing spatial candidates of a mergecandidate list of a current block.

FIG. 23 is a diagram for describing a history-based motion vectorcandidate list of a merge candidate list of a current block.

FIG. 24A is a diagram for describing pairwise average candidatesaccording to another embodiment, FIG. 24B is a diagram for describing amethod of adding a zero motion vector candidate in a pairwise averagecandidate configuration process according to another embodiment, andFIG. 24C is a diagram for describing a method of adding a half-sizemerge candidate in a pairwise average candidate configuration processaccording to another embodiment.

BEST MODE

A video decoding method according to an embodiment of the disclosure mayinclude: when a merge candidate list of a current block is configured,determining whether the number of merge candidates included in the mergecandidate list is greater than 1 and is smaller than a predeterminedmaximum merge candidate number; when the number of the merge candidatesincluded in the merge candidate list is greater than 1 and is smallerthan the predetermined maximum merge candidate number, obtaining anadditional merge candidate by using a first merge candidate and a secondmerge candidate of the merge candidate list of the current block;updating the merge candidate list by adding the obtained additionalmerge candidate to the merge candidate list; and performing predictionon the current block, based on the merge candidate list.

According to an embodiment, the additional merge candidate may comprisea motion vector having an average value of the first merge candidatemotion vector and the second merge candidate motion vector.

According to an embodiment, the first merge candidate and the secondmerge candidate may each include at least one of spatial candidatesbeing spatially adjacent to the current block, a temporal candidatebeing temporally adjacent to the current block, and motion vectorcandidates included in a history-based motion vector candidate listincluding a plurality of pieces of motion information of blocks encodedin a merge mode before the current block.

According to an embodiment, the spatial candidates being spatiallyadjacent to the current block may include at least one of a leftadjacent block, an upper adjacent block, a lower-left adjacent block, anupper-right adjacent block, and an upper-left adjacent block whichneighbor the current block.

According to an embodiment, after the additional merge candidate isadded to the merge candidate list, when the number of merge candidatesincluded in the merge candidate list is smaller than the predeterminedmaximum merge candidate number, a zero motion vector may be added to themerge candidate list.

A video encoding method according to an embodiment of the disclosure mayinclude: when a merge candidate list of a current block is configured,determining whether the number of merge candidates included in the mergecandidate list is greater than 1 and is smaller than a predeterminedmaximum merge candidate number; when the number of the merge candidatesincluded in the merge candidate list is greater than 1 and is smallerthan the predetermined maximum merge candidate number, obtaining anadditional merge candidate by using a first merge candidate and a secondmerge candidate of the merge candidate list of the current block;updating the merge candidate list by adding the obtained additionalmerge candidate to the merge candidate list; and performing predictionon the current block, based on the merge candidate list.

According to an embodiment, the additional merge candidate may comprisea motion vector having an average value of the first merge candidatemotion vector and the second merge candidate motion vector.

According to an embodiment, the first merge candidate and the secondmerge candidate may each include at least one of spatial candidatesbeing spatially adjacent to the current block, a temporal candidatebeing temporally adjacent to the current block, and motion vectorcandidates included in a history-based motion vector candidate listincluding a plurality of pieces of motion information of blocks encodedin a merge mode before the current block.

According to an embodiment, the spatial candidates being spatiallyadjacent to the current block may include at least one of a leftadjacent block, an upper adjacent block, a lower-left adjacent block, anupper-right adjacent block, and an upper-left adjacent block whichneighbor the current block.

According to an embodiment, after the additional merge candidate isadded to the merge candidate list, when the number of merge candidatesincluded in the merge candidate list is smaller than the predeterminedmaximum merge candidate number, a zero motion vector may be added to themerge candidate list.

A video decoding apparatus according to an embodiment of the disclosuremay include: a memory; and at least one processor connected to thememory, wherein the at least one processor is configured to, when amerge candidate list of a current block is configured, determine whetherthe number of merge candidates included in the merge candidate list isgreater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, obtain an additional mergecandidate by using a first merge candidate and a second merge candidateof the merge candidate list of the current block, update the mergecandidate list by adding the obtained additional merge candidate to themerge candidate list, and perform prediction on the current block, basedon the merge candidate list.

According to an embodiment, the additional merge candidate may comprisea motion vector having an average value of the first merge candidatemotion vector and the second merge candidate motion vector.

According to an embodiment, the first merge candidate and the secondmerge candidate may each include at least one of spatial candidatesbeing spatially adjacent to the current block, a temporal candidatebeing temporally adjacent to the current block, and motion vectorcandidates included in a history-based motion vector candidate listincluding a plurality of pieces of motion information of blocks encodedin a merge mode before the current block.

According to an embodiment, the spatial candidates being spatiallyadjacent to the current block may include at least one of a leftadjacent block, an upper adjacent block, a lower-left adjacent block, anupper-right adjacent block, and an upper-left adjacent block whichneighbor the current block.

According to an embodiment, after the additional merge candidate isadded to the merge candidate list, when the number of merge candidatesincluded in the merge candidate list is smaller than the predeterminedmaximum merge candidate number, a zero motion vector may be added to themerge candidate list.

Mode of Disclosure

Advantages and features of embodiments and methods of accomplishing thesame may be understood more readily by reference to the embodiments andthe accompanying drawings. In this regard, the disclosure may havedifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe concept of the disclosure to one of ordinary skill in the art.

The terms used in the specification will be briefly defined, and theembodiments will be described in detail.

All terms including descriptive or technical terms which are used in thespecification should be construed as having meanings that are obvious toone of ordinary skill in the art. However, the terms may have differentmeanings according to the intention of one of ordinary skill in the art,precedent cases, or the appearance of new technologies. Also, some termsmay be arbitrarily selected by the applicant, and in this case, themeaning of the selected terms will be described in detail in thedetailed description of the disclosure. Therefore, the terms used in thedisclosure should not be interpreted based on only their names but haveto be defined based on the meaning of the terms together with thedescriptions throughout the specification.

In the following specification, the singular forms include plural formsunless the context clearly indicates otherwise.

When a part “includes” or “comprises” an element, unless there is aparticular description contrary thereto, the part may further includeother elements, not excluding the other elements.

In the following description, terms such as “unit” indicate a softwareor hardware component and the “unit” performs certain functions.However, the “unit” is not limited to software or hardware. The “unit”may be formed so as to be in an addressable storage medium, or may beformed so as to operate one or more processors. Thus, for example, theterm “unit” may refer to components such as software components,object-oriented software components, class components, and taskcomponents, and may include processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,micro codes, circuits, data, a database, data structures, tables,arrays, and variables. A function provided by the components and “units”may be associated with a smaller number of components and “units”, ormay be divided into additional components and “units”.

According to an embodiment of the disclosure, the “unit” may include aprocessor and a memory. The term “processor” should be interpretedbroadly to include a general purpose processor, a central processingunit (CPU), a microprocessor, a digital signal processor (DSP), acontroller, a microcontroller, a state machine, and the like. In someenvironments, the “processor” may refer to an application specificsemiconductor (ASIC), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), or the like. The term “processor” mayrefer to a combination of processing devices such as, for example, acombination of a DSP and a microprocessor, a combination of a pluralityof microprocessors, a combination of one or more microprocessors inconjunction with a DSP core, or a combination of any other suchconfigurations.

The term “memory” should be interpreted broadly to include anyelectronic component capable of storing electronic information. The term“memory” may refer to various types of processor-readable media, such asa random access memory (RAM), a read-only memory (ROM), a non-volatilerandom access memory (NVRAM), a programmable read-only memory (PROM), anerase-programmable read-only memory (EPROM), an electrically erasablePROM (EEPROM), a flash memory, a magnetic or optical data storagedevice, registers, and the like. When the processor can read informationfrom a memory and/or write information to the memory, the memory is saidto be in an electronic communication state with the processor. Thememory integrated in the processor is in an electronic communicationstate with the processor.

Hereinafter, an “image” may be a static image such as a still image of avideo or may be a dynamic image such as a moving image, that is, thevideo itself.

Hereinafter, a “sample” denotes data assigned to a sampling position ofan image, i.e., data to be processed. For example, pixel values of animage in a spatial domain and transform coefficients on a transformdomain may be samples A unit including at least one such sample may bedefined as a block.

Also, in the present specification, a “current block” may denote a blockof a largest coding unit, a coding unit, a prediction unit, or atransform unit of a current image to be encoded or decoded.

Hereinafter, the disclosure will now be described more fully withreference to the accompanying drawings for one of ordinary skill in theart to be able to perform the embodiments without any difficulty. Inaddition, portions irrelevant to the description will be omitted in thedrawings for a clear description of the disclosure.

Hereinafter, an image encoding apparatus, an image decoding apparatus,an image encoding method, and an image decoding method, according to anembodiment, will be described with reference to FIGS. 1 to 16 . Withreference to FIGS. 3 to 16 , a method of determining a data unit of animage according to an embodiment will be described, with reference toFIGS. 17 to 23 , a video encoding/decoding method according to anembodiment will be described, the encoding/decoding method involving,when a merge candidate list of a current block is configured,determining whether the number of merge candidates included in the mergecandidate list is greater than 1 and is smaller than a predeterminedmaximum merge candidate number, when the number of the merge candidatesincluded in the merge candidate list is greater than 1 and is smallerthan the predetermined maximum merge candidate number, obtaining anadditional merge candidate by using a first merge candidate and a secondmerge candidate of the merge candidate list of the current block, addingthe obtained additional merge candidate to the merge candidate list toupdate the merge candidate list, and performing prediction on thecurrent block, based on the merge candidate list, and with reference toFIGS. 24A to 24C, a method of adding pairwise average candidates to amerge candidate list according to another embodiment will be described.

Hereinafter, a method and apparatus for adaptively selecting a contextmodel, based on various shapes of coding units, according to anembodiment of the disclosure, will be described with reference to FIGS.1 and 2 .

FIG. 1 illustrates a schematic block diagram of an image decodingapparatus according to an embodiment.

The image decoding apparatus 100 may include a receiver 110 and adecoder 120. The receiver 110 and the decoder 120 may include at leastone processor. Also, the receiver 110 and the decoder 120 may include amemory storing instructions to be performed by the at least oneprocessor.

The receiver 110 may receive a bitstream. The bitstream includesinformation of an image encoded by an image encoding apparatus 2200described below. Also, the bitstream may be transmitted from the imageencoding apparatus 2200. The image encoding apparatus 2200 and the imagedecoding apparatus 100 may be connected via wires or wirelessly, and thereceiver 110 may receive the bitstream via wires or wirelessly. Thereceiver 110 may receive the bitstream from a storage medium, such as anoptical medium or a hard disk. The decoder 120 may reconstruct an imagebased on information obtained from the received bitstream. The decoder120 may obtain, from the bitstream, a syntax element for reconstructingthe image. The decoder 120 may reconstruct the image based on the syntaxelement.

Operations of the image decoding apparatus 100 will be described indetail with reference to FIG. 2 .

FIG. 2 illustrates a flowchart of an image decoding method according toan embodiment.

According to an embodiment of the disclosure, the receiver 110 receivesa bitstream.

The image decoding apparatus 100 obtains, from a bitstream, a bin stringcorresponding to a split shape mode of a coding unit (operation 210).The image decoding apparatus 100 determines a split rule of coding units(operation 220). Also, the image decoding apparatus 100 splits thecoding unit into a plurality of coding units, based on at least one ofthe bin string corresponding to the split shape mode and the split rule(operation 230). The image decoding apparatus 100 may determine anallowable first range of a size of the coding unit, according to a ratioof the width and the height of the coding unit, so as to determine thesplit rule. The image decoding apparatus 100 may determine an allowablesecond range of the size of the coding unit, according to the splitshape mode of the coding unit, so as to determine the split rule.

Hereinafter, splitting of a coding unit will be described in detailaccording to an embodiment of the disclosure.

First, one picture may be split into one or more slices or one or moretiles. One slice or one tile may be a sequence of one or more largestcoding units (coding tree units (CTUs)). There is a largest coding block(coding tree block (CTB)) conceptually compared to a largest coding unit(CTU).

The largest coding block (CTB) denotes an N×N block including N×Nsamples (where N is an integer). Each color component may be split intoone or more largest coding blocks.

When a picture has three sample arrays (sample arrays for Y, Cr, and Cbcomponents), a largest coding unit (CTU) includes a largest coding blockof a luma sample, two corresponding largest coding blocks of chromasamples, and syntax structures used to encode the luma sample and thechroma samples. When a picture is a monochrome picture, a largest codingunit includes a largest coding block of a monochrome sample and syntaxstructures used to encode the monochrome samples. When a picture is apicture encoded in color planes separated according to color components,a largest coding unit includes syntax structures used to encode thepicture and samples of the picture.

One largest coding block (CTB) may be split into M×N coding blocksincluding M×N samples (M and N are integers).

When a picture has sample arrays for Y, Cr, and Cb components, a codingunit (CU) includes a coding block of a luma sample, two correspondingcoding blocks of chroma samples, and syntax structures used to encodethe luma sample and the chroma samples. When a picture is a monochromepicture, a coding unit includes a coding block of a monochrome sampleand syntax structures used to encode the monochrome samples. When apicture is a picture encoded in color planes separated according tocolor components, a coding unit includes syntax structures used toencode the picture and samples of the picture.

As described above, a largest coding block and a largest coding unit areconceptually distinguished from each other, and a coding block and acoding unit are conceptually distinguished from each other. That is, a(largest) coding unit refers to a data structure including a (largest)coding block including a corresponding sample and a syntax structurecorresponding to the (largest) coding block. However, because it isunderstood by one of ordinary skill in the art that a (largest) codingunit or a (largest) coding block refers to a block of a predeterminedsize including a predetermined number of samples, a largest coding blockand a largest coding unit, or a coding block and a coding unit arementioned in the following specification without being distinguishedunless otherwise described.

An image may be split into largest coding units (CTUs). A size of eachlargest coding unit may be determined based on information obtained froma bitstream. A shape of each largest coding unit may be a square shapeof the same size. However, the embodiment is not limited thereto.

For example, information about a maximum size of a luma coding block maybe obtained from a bitstream. For example, the maximum size of the lumacoding block indicated by the information about the maximum size of theluma coding block may be one of 4×4, 8×8, 16×16, 32×32, 64×64, 128×128,and 256×256.

For example, information about a luma block size difference and amaximum size of a luma coding block that may be split into two may beobtained from a bitstream. The information about the luma block sizedifference may refer to a size difference between a luma largest codingunit and a largest luma coding block that may be split into two.Accordingly, when the information about the maximum size of the lumacoding block that may be split into two and the information about theluma block size difference obtained from the bitstream are combined witheach other, a size of the luma largest coding unit may be determined. Asize of a chroma largest coding unit may be determined by using the sizeof the luma largest coding unit. For example, when a Y:Cb:Cr ratio is4:2:0 according to a color format, a size of a chroma block may be halfa size of a luma block, and a size of a chroma largest coding unit maybe half a size of a luma largest coding unit.

According to an embodiment, because information about a maximum size ofa luma coding block that is binary splittable is obtained from abitstream, the maximum size of the luma coding block that is binarysplittable may be variably determined. In contrast, a maximum size of aluma coding block that is ternary splittable may be fixed. For example,the maximum size of the luma coding block that is ternary splittable inan I-picture may be 32×32, and the maximum size of the luma coding blockthat is ternary splittable in a P-picture or a B-picture may be 64×64.

Also, a largest coding unit may be hierarchically split into codingunits based on split shape mode information obtained from a bitstream.At least one of information indicating whether quad splitting isperformed, information indicating whether multi-splitting is performed,split direction information, and split type information may be obtainedas the split shape mode information from the bitstream.

For example, the information indicating whether quad splitting isperformed may indicate whether a current coding unit is quad split(QUAD_SPLIT) or not.

When the current coding unit is not quad split, the informationindicating whether multi-splitting is performed may indicate whether thecurrent coding unit is no longer split (NO_SPLIT) or binary/ternarysplit.

When the current coding unit is binary split or ternary split, the splitdirection information indicates that the current coding unit is split inone of a horizontal direction and a vertical direction.

When the current coding unit is split in the horizontal direction or thevertical direction, the split type information indicates that thecurrent coding unit is binary split or ternary split.

A split mode of the current coding unit may be determined according tothe split direction information and the split type information. A splitmode when the current coding unit is binary split in the horizontaldirection may be determined to be a binary horizontal split mode(SPLIT_BT_HOR), a split mode when the current coding unit is ternarysplit in the horizontal direction may be determined to be a ternaryhorizontal split mode (SPLIT_TT_HOR), a split mode when the currentcoding unit is binary split in the vertical direction may be determinedto be a binary vertical split mode (SPLIT_BT_VER), and a split mode whenthe current coding unit is ternary split in the vertical direction maybe determined to be a ternary vertical split mode (SPLIT_TT_VER).

The image decoding apparatus 100 may obtain, from the bitstream, thesplit shape mode information from one bin string. A form of thebitstream received by the image decoding apparatus 100 may include fixedlength binary code, unary code, truncated unary code, predeterminedbinary code, or the like. The bin string is information in a binarynumber. The bin string may include at least one bit. The image decodingapparatus 100 may obtain the split shape mode information correspondingto the bin string, based on the split rule. The image decoding apparatus100 may determine whether to quad split a coding unit, whether not tosplit a coding unit, a split direction, and a split type, based on onebin string.

The coding unit may be smaller than or the same as the largest codingunit. For example, because a largest coding unit is a coding unit havinga maximum size, the largest coding unit is one of coding units. Whensplit shape mode information about a largest coding unit indicates thatsplitting is not performed, a coding unit determined in the largestcoding unit has the same size as that of the largest coding unit. Whensplit shape mode information about a largest coding unit indicates thatsplitting is performed, the largest coding unit may be split into codingunits. Also, when split shape mode information about a coding unitindicates that splitting is performed, the coding unit may be split intosmaller coding units. However, the splitting of the image is not limitedthereto, and the largest coding unit and the coding unit may not bedistinguished. The splitting of the coding unit will be described indetail with reference to FIGS. 3 to 16 .

Also, one or more prediction blocks for prediction may be determinedfrom a coding unit. The prediction block may be the same as or smallerthan the coding unit. Also, one or more transform blocks fortransformation may be determined from a coding unit. The transform blockmay be the same as or smaller than the coding unit.

The shapes and sizes of the transform block and prediction block may notbe related to each other.

In another embodiment, prediction may be performed by using a codingunit as a prediction unit. Also, transformation may be performed byusing a coding unit as a transform block.

The splitting of the coding unit will be described in detail withreference to FIGS. 3 to 16 . A current block and an adjacent block ofthe disclosure may indicate one of the largest coding unit, the codingunit, the prediction block, and the transform block. Also, the currentblock of the current coding unit is a block that is currently beingdecoded or encoded or a block that is currently being split. Theadjacent block may be a block reconstructed before the current block.The adjacent block may be adjacent to the current block spatially ortemporally. The adjacent block may be located at one of the lower left,left, upper left, top, upper right, right, lower right of the currentblock.

FIG. 3 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a current codingunit, according to an embodiment.

A block shape may include 4N×4N, 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N,16N×N, N×16N, 8N×N, or N×8N. Here, N may be a positive integer. Blockshape information is information indicating at least one of a shape, adirection, a ratio of width and height, or size of a coding unit.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are the same(i.e., when the block shape of the coding unit is 4N×4N), the imagedecoding apparatus 100 may determine the block shape information of thecoding unit as a square. The image decoding apparatus 100 may determinethe shape of the coding unit to be a non-square.

When the width and the height of the coding unit are different from eachother (i.e., when the block shape of the coding unit is 4N×2N, 2N×4N,4N×N, N×4N, 32N×N, N×32N, 16N×N, N×16N, 8N×N, or N×8N), the imagedecoding apparatus 100 may determine the block shape information of thecoding unit as a non-square shape. When the shape of the coding unit isnon-square, the image decoding apparatus 100 may determine the ratio ofthe width and height among the block shape information of the codingunit to be at least one of 1:2, 2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1,1:32, and 32:1. Also, the image decoding apparatus 100 may determinewhether the coding unit is in a horizontal direction or a verticaldirection, based on the length of the width and the length of the heightof the coding unit. Also, the image decoding apparatus 100 may determinethe size of the coding unit, based on at least one of the length of thewidth, the length of the height, or the area of the coding unit.

According to an embodiment, the image decoding apparatus 100 maydetermine the shape of the coding unit by using the block shapeinformation, and may determine a splitting method of the coding unit byusing the split shape mode information. That is, a coding unit splittingmethod indicated by the split shape mode information may be determinedbased on a block shape indicated by the block shape information used bythe image decoding apparatus 100.

The image decoding apparatus 100 may obtain the split shape modeinformation from a bitstream. However, an embodiment is not limitedthereto, and the image decoding apparatus 100 and the image encodingapparatus 2200 may determine pre-agreed split shape mode information,based on the block shape information. The image decoding apparatus 100may determine the pre-agreed split shape mode information with respectto a largest coding unit or a minimum coding unit. For example, theimage decoding apparatus 100 may determine split shape mode informationwith respect to the largest coding unit to be a quad split. Also, theimage decoding apparatus 100 may determine split shape mode informationregarding the smallest coding unit to be “not to perform splitting”. Inparticular, the image decoding apparatus 100 may determine the size ofthe largest coding unit to be 256×256. The image decoding apparatus 100may determine the pre-agreed split shape mode information to be a quadsplit. The quad split is a split shape mode in which the width and theheight of the coding unit are both bisected. The image decodingapparatus 100 may obtain a coding unit of a 128×128 size from thelargest coding unit of a 256×256 size, based on the split shape modeinformation. Also, the image decoding apparatus 100 may determine thesize of the smallest coding unit to be 4×4. The image decoding apparatus100 may obtain split shape mode information indicating “not to performsplitting” with respect to the smallest coding unit.

According to an embodiment, the image decoding apparatus 100 may use theblock shape information indicating that the current coding unit has asquare shape. For example, the image decoding apparatus 100 maydetermine whether not to split a square coding unit, whether tovertically split the square coding unit, whether to horizontally splitthe square coding unit, or whether to split the square coding unit intofour coding units, based on the split shape mode information. Referringto FIG. 3 , when the block shape information of a current coding unit300 indicates a square shape, the decoder 120 may determine that acoding unit 310 a having the same size as the current coding unit 300 isnot split, based on the split shape mode information indicating not toperform splitting, or may determine coding units 310 b, 310 c, 310 d,310 e, or 310 f split based on the split shape mode informationindicating a predetermined splitting method.

Referring to FIG. 3 , according to an embodiment, the image decodingapparatus 100 may determine two coding units 310 b obtained by splittingthe current coding unit 300 in a vertical direction, based on the splitshape mode information indicating to perform splitting in a verticaldirection. The image decoding apparatus 100 may determine two codingunits 310 c obtained by splitting the current coding unit 300 in ahorizontal direction, based on the split shape mode informationindicating to perform splitting in a horizontal direction. The imagedecoding apparatus 100 may determine four coding units 310 d obtained bysplitting the current coding unit 300 in vertical and horizontaldirections, based on the split shape mode information indicating toperform splitting in vertical and horizontal directions. According to anembodiment, the image decoding apparatus 100 may determine three codingunits 310 e obtained by splitting the current coding unit 300 in avertical direction, based on the split shape mode information indicatingto perform ternary splitting in a vertical direction. The image decodingapparatus 100 may determine three coding units 310 f obtained bysplitting the current coding unit 300 in a horizontal direction, basedon the split shape mode information indicating to perform ternarysplitting in a horizontal direction. However, splitting methods of thesquare coding unit are not limited to the above-described methods, andthe split shape mode information may indicate various methods.Predetermined splitting methods of splitting the square coding unit willbe described in detail below in relation to various embodiments.

FIG. 4 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a non-square codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may useblock shape information indicating that a current coding unit has anon-square shape. The image decoding apparatus 100 may determine whethernot to split the non-square current coding unit or whether to split thenon-square current coding unit by using a predetermined splittingmethod, based on split shape mode information. Referring to FIG. 4 ,when the block shape information of a current coding unit 400 or 450indicates a non-square shape, the image decoding apparatus 100 maydetermine a coding unit 410 or 460 having the same size as the currentcoding unit 400 or 450, based on the split shape mode informationindicating not to perform splitting, or may determine coding units 420 aand 420 b, 430 a to 430 c, 470 a and 470 b, or 480 a to 480 c splitbased on the split shape mode information indicating a predeterminedsplitting method. Predetermined splitting methods of splitting anon-square coding unit will be described in detail below in relation tovarious embodiments.

According to an embodiment, the image decoding apparatus 100 maydetermine a splitting method of a coding unit by using the split shapemode information and, in this case, the split shape mode information mayindicate the number of one or more coding units generated by splitting acoding unit. Referring to FIG. 4 , when the split shape mode informationindicates to split the current coding unit 400 or 450 into two codingunits, the image decoding apparatus 100 may determine two coding units420 a and 420 b, or 470 a and 470 b included in the current coding unit400 or 450, by splitting the current coding unit 400 or 450 based on thesplit shape mode information.

According to an embodiment, when the image decoding apparatus 100 splitsthe non-square current coding unit 400 or 450 based on the split shapemode information, the image decoding apparatus 100 may consider thelocation of a long side of the non-square current coding unit 400 or 450to split a current coding unit. For example, the image decodingapparatus 100 may determine a plurality of coding units by splitting thecurrent coding unit 400 or 450 in a direction of splitting a long sideof the current coding unit 400 or 450, in consideration of the shape ofthe current coding unit 400 or 450.

According to an embodiment, when the split shape mode informationindicates to split (ternary split) a coding unit into an odd number ofblocks, the image decoding apparatus 100 may determine an odd number ofcoding units included in the current coding unit 400 or 450. Forexample, when the split shape mode information indicates to split thecurrent coding unit 400 or 450 into three coding units, the imagedecoding apparatus 100 may split the current coding unit 400 or 450 intothree coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c.

According to an embodiment, a ratio of the width and height of thecurrent coding unit 400 or 450 may be 4:1 or 1:4. When the ratio of thewidth and height is 4:1, the block shape information may indicate ahorizontal direction because the length of the width is longer than thelength of the height. When the ratio of the width and height is 1:4, theblock shape information may indicate a vertical direction because thelength of the width is shorter than the length of the height. The imagedecoding apparatus 100 may determine to split a current coding unit intoan odd number of blocks, based on the split shape mode information.Also, the image decoding apparatus 100 may determine a split directionof the current coding unit 400 or 450, based on the block shapeinformation of the current coding unit 400 or 450. For example, when thecurrent coding unit 400 is in the vertical direction, the image decodingapparatus 100 may determine the coding units 430 a, 430 b, and 430 c bysplitting the current coding unit 400 in the horizontal direction. Also,when the current coding unit 450 is in the horizontal direction, theimage decoding apparatus 100 may determine the coding units 480 a, 480b, and 480 c by splitting the current coding unit 450 in the verticaldirection.

According to an embodiment, the image decoding apparatus 100 maydetermine an odd number of coding units included in the current codingunit 400 or 450, and not all the determined coding units may have thesame size. For example, a predetermined coding unit 430 b or 480 b fromamong the determined odd number of coding units 430 a, 430 b, and 430 c,or 480 a, 480 b, and 480 c may have a size different from the size ofthe other coding units 430 a and 430 c, or 480 a and 480 c. That is,coding units which may be determined by splitting the current codingunit 400 or 450 may have multiple sizes and, in some cases, all of theodd number of coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and480 c may have different sizes.

According to an embodiment, when the split shape mode informationindicates to split a coding unit into the odd number of blocks, theimage decoding apparatus 100 may determine the odd number of codingunits included in the current coding unit 400 or 450, and moreover, mayput a predetermined restriction on at least one coding unit from amongthe odd number of coding units generated by splitting the current codingunit 400 or 450. Referring to FIG. 4 , the image decoding apparatus 100may set a decoding process regarding the coding unit 430 b or 480 blocated at the center among the three coding units 430 a, 430 b, and 430c, or 480 a, 480 b, and 480 c generated as the current coding unit 400or 450 is split to be different from that of the other coding units 430a and 430 c, or 480 a and 480 c. For example, the image decodingapparatus 100 may restrict the coding unit 430 b or 480 b at the centerlocation to be no longer split or to be split only a predeterminednumber of times, unlike the other coding units 430 a and 430 c, or 480 aand 480 c.

FIG. 5 illustrates a process, performed by an image decoding apparatus,of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split or to not split a square first coding unit 500 intocoding units, based on at least one of the block shape information andthe split shape mode information. According to an embodiment, when thesplit shape mode information indicates to split the first coding unit500 in a horizontal direction, the image decoding apparatus 100 maydetermine a second coding unit 510 by splitting the first coding unit500 in a horizontal direction. A first coding unit, a second codingunit, and a third coding unit used according to an embodiment are termsused to understand a relation before and after splitting a coding unit.For example, a second coding unit may be determined by splitting a firstcoding unit, and a third coding unit may be determined by splitting thesecond coding unit. It will be understood that the relation of the firstcoding unit, the second coding unit, and the third coding unit followsthe above descriptions.

According to an embodiment, the image decoding apparatus 100 maydetermine to split or to not split the determined second coding unit 510into coding units, based on the split shape mode information. Referringto FIG. 5 , the image decoding apparatus 100 may split the non-squaresecond coding unit 510, which is determined by splitting the firstcoding unit 500, into one or more third coding units 520 a, 520 b, 520c, and 520 d based on at least one of the split shape mode informationand the split shape mode information, or may not split the non-squaresecond coding unit 510. The image decoding apparatus 100 may obtain thesplit shape mode information, and may obtain a plurality ofvarious-shaped second coding units (e.g., 510) by splitting the firstcoding unit 500, based on the obtained split shape mode information, andthe second coding unit 510 may be split by using a splitting method ofthe first coding unit 500 based on the split shape mode information.According to an embodiment, when the first coding unit 500 is split intothe second coding units 510 based on the split shape mode information ofthe first coding unit 500, the second coding unit 510 may also be splitinto the third coding units (e.g., 520 a, or 520 b, 520 c, and 520 d)based on the split shape mode information of the second coding unit 510.That is, a coding unit may be recursively split based on the split shapemode information of each coding unit. Therefore, a square coding unitmay be determined by splitting a non-square coding unit, and anon-square coding unit may be determined by recursively splitting thesquare coding unit.

Referring to FIG. 5 , a predetermined coding unit (e.g., a coding unitlocated at a center location, or a square coding unit) from among an oddnumber of third coding units 520 b, 520 c, and 520 d determined bysplitting the non-square second coding unit 510 may be recursivelysplit. According to an embodiment, the square third coding unit 520 bfrom among the odd number of third coding units 520 b, 520 c, and 520 dmay be split in a horizontal direction into a plurality of fourth codingunits. A non-square fourth coding unit 530 b or 530 d from among theplurality of fourth coding units 530 a, 530 b, 530 c, and 530 d may bere-split into a plurality of coding units. For example, the non-squarefourth coding unit 530 b or 530 d may be re-split into an odd number ofcoding units. A method that may be used to recursively split a codingunit will be described below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may spliteach of the third coding units 520 a, or 520 b, 520 c, and 520 d intocoding units, based on the split shape mode information. Also, the imagedecoding apparatus 100 may determine to not split the second coding unit510 based on the split shape mode information. According to anembodiment, the image decoding apparatus 100 may split the non-squaresecond coding unit 510 into the odd number of third coding units 520 b,520 c, and 520 d. The image decoding apparatus 100 may put apredetermined restriction on a predetermined third coding unit fromamong the odd number of third coding units 520 b, 520 c, and 520 d. Forexample, the image decoding apparatus 100 may restrict the third codingunit 520 c at a center location from among the odd number of thirdcoding units 520 b, 520 c, and 520 d to be no longer split or to besplit a settable number of times.

Referring to FIG. 5 , the image decoding apparatus 100 may restrict thethird coding unit 520 c, which is at the center location from among theodd number of third coding units 520 b, 520 c, and 520 d included in thenon-square second coding unit 510, to be no longer split, to be split byusing a predetermined splitting method (e.g., split into only fourcoding units or split by using a splitting method of the second codingunit 510), or to be split only a predetermined number of times (e.g.,split only n times (where n>0)). However, the restrictions on the thirdcoding unit 520 c at the center location are not limited to theabove-described examples, and may include various restrictions fordecoding the third coding unit 520 c at the center location differentlyfrom the other third coding units 520 b and 520 d.

According to an embodiment, the image decoding apparatus 100 may obtainthe split shape mode information, which is used to split a currentcoding unit, from a predetermined location in the current coding unit.

FIG. 6 illustrates a method, performed by an image decoding apparatus,of determining a predetermined coding unit from among an odd number ofcoding units, according to an embodiment.

Referring to FIG. 6 , split shape mode information of a current codingunit 600 or 650 may be obtained from a sample of a predeterminedlocation (e.g., a sample 640 or 690 of a center location) from among aplurality of samples included in the current coding unit 600 or 650.However, the predetermined location in the current coding unit 600, fromwhich at least one piece of the split shape mode information may beobtained, is not limited to the center location in FIG. 6 , and mayinclude various locations included in the current coding unit 600 (e.g.,top, bottom, left, right, upper left, lower left, upper right, lowerright locations, or the like). The image decoding apparatus 100 mayobtain the split shape mode information from the predetermined locationand may determine to split or to not split the current coding unit intovarious-shaped and various-sized coding units.

According to an embodiment, when the current coding unit is split into apredetermined number of coding units, the image decoding apparatus 100may select one of the coding units. Various methods may be used toselect one of a plurality of coding units, as will be described below inrelation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit into a plurality of coding units, and maydetermine a coding unit at a predetermined location.

According to an embodiment, image decoding apparatus 100 may useinformation indicating locations of the odd number of coding units, todetermine a coding unit at a center location from among the odd numberof coding units. Referring to FIG. 6 , the image decoding apparatus 100may determine the odd number of coding units 620 a, 620 b, and 620 c orthe odd number of coding units 660 a, 660 b, and 660 c by splitting thecurrent coding unit 600 or the current coding unit 650. The imagedecoding apparatus 100 may determine the middle coding unit 620 b or themiddle coding unit 660 b by using information about the locations of theodd number of coding units 620 a, 620 b, and 620 c or the odd number ofcoding units 660 a, 660 b, and 660 c. For example, the image decodingapparatus 100 may determine the coding unit 620 b of the center locationby determining the locations of the coding units 620 a, 620 b, and 620 cbased on information indicating locations of predetermined samplesincluded in the coding units 620 a, 620 b, and 620 c. In detail, theimage decoding apparatus 100 may determine the coding unit 620 b at thecenter location by determining the locations of the coding units 620 a,620 b, and 620 c based on information indicating locations of upper-leftsamples 630 a, 630 b, and 630 c of the coding units 620 a, 620 b, and620 c.

According to an embodiment, the information indicating the locations ofthe upper-left samples 630 a, 630 b, and 630 c, which are included inthe coding units 620 a, 620 b, and 620 c, respectively, may includeinformation about locations or coordinates of the coding units 620 a,620 b, and 620 c in a picture. According to an embodiment, theinformation indicating the locations of the upper-left samples 630 a,630 b, and 630 c, which are included in the coding units 620 a, 620 b,and 620 c, respectively, may include information indicating widths orheights of the coding units 620 a, 620 b, and 620 c included in thecurrent coding unit 600, and the widths or heights may correspond toinformation indicating differences between the coordinates of the codingunits 620 a, 620 b, and 620 c in the picture. That is, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation by directly using the information about the locations orcoordinates of the coding units 620 a, 620 b, and 620 c in the picture,or by using the information about the widths or heights of the codingunits, which correspond to the difference values between thecoordinates.

According to an embodiment, information indicating the location of theupper-left sample 630 a of the upper coding unit 620 a may includecoordinates (xa, ya), information indicating the location of theupper-left sample 630 b of the center coding unit 620 b may includecoordinates (xb, yb), and information indicating the location of theupper-left sample 630 c of the lower coding unit 620 c may includecoordinates (xc, yc). The image decoding apparatus 100 may determine themiddle coding unit 620 b by using the coordinates of the upper-leftsamples 630 a, 630 b, and 630 c which are included in the coding units620 a, 620 b, and 620 c, respectively. For example, when the coordinatesof the upper-left samples 630 a, 630 b, and 630 c are sorted in anascending or descending order, the coding unit 620 b including thecoordinates (xb, yb) of the sample 630 b at a center location may bedetermined as a coding unit at a center location from among the codingunits 620 a, 620 b, and 620 c determined by splitting the current codingunit 600. However, the coordinates indicating the locations of theupper-left samples 630 a, 630 b, and 630 c may include coordinatesindicating absolute locations in the picture, or may use coordinates(dxb, dyb) indicating a relative location of the upper-left sample 630 bof the middle coding unit 620 b and coordinates (dxc, dyc) indicating arelative location of the upper-left sample 630 c of the lower codingunit 620 c with reference to the location of the upper-left sample 630 aof the upper coding unit 620 a. A method of determining a coding unit ata predetermined location by using coordinates of a sample included inthe coding unit, as information indicating a location of the sample, isnot limited to the above-described method, and may include variousarithmetic methods capable of using the coordinates of the sample.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit 600 into a plurality of coding units 620 a, 620b, and 620 c, and may select one of the coding units 620 a, 620 b, and620 c based on a predetermined criterion. For example, the imagedecoding apparatus 100 may select the coding unit 620 b, which has asize different from that of the others, from among the coding units 620a, 620 b, and 620 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width or height of each of the coding units 620 a, 620 b,and 620 c by using the coordinates (xa, ya) that is the informationindicating the location of the upper-left sample 630 a of the uppercoding unit 620 a, the coordinates (xb, yb) that is the informationindicating the location of the upper-left sample 630 b of the middlecoding unit 620 b, and the coordinates (xc, yc) that are the informationindicating the location of the upper-left sample 630 c of the lowercoding unit 620 c. The image decoding apparatus 100 may determine therespective sizes of the coding units 620 a, 620 b, and 620 c by usingthe coordinates (xa, ya), (xb, yb), and (xc, yc) indicating thelocations of the coding units 620 a, 620 b, and 620 c. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe upper coding unit 620 a to be the width of the current coding unit600. The image decoding apparatus 100 may determine the height of theupper coding unit 620 a to be yb-ya. According to an embodiment, theimage decoding apparatus 100 may determine the width of the middlecoding unit 620 b to be the width of the current coding unit 600. Theimage decoding apparatus 100 may determine the height of the middlecoding unit 620 b to be yc-yb. According to an embodiment, the imagedecoding apparatus 100 may determine the width or height of the lowercoding unit 620 c by using the width or height of the current codingunit 600 or the widths or heights of the upper and middle coding units620 a and 620 b. The image decoding apparatus 100 may determine a codingunit, which has a size different from that of the others, based on thedetermined widths and heights of the coding units 620 a, 620 b, and 620c. Referring to FIG. 6 , the image decoding apparatus 100 may determinethe middle coding unit 620 b, which has a size different from the sizeof the upper and lower coding units 620 a and 620 c, as the coding unitof the predetermined location. However, the above-described method,performed by the image decoding apparatus 100, of determining a codingunit having a size different from the size of the other coding unitsmerely corresponds to an example of determining a coding unit at apredetermined location by using the sizes of coding units, which aredetermined based on coordinates of samples, and thus various methods ofdetermining a coding unit at a predetermined location by comparing thesizes of coding units, which are determined based on coordinates ofpredetermined samples, may be used.

The image decoding apparatus 100 may determine the width or height ofeach of the coding units 660 a, 660 b, and 660 c by using thecoordinates (xd, yd) that are information indicating the location of anupper-left sample 670 a of the left coding unit 660 a, the coordinates(xe, ye) that are information indicating the location of an upper-leftsample 670 b of the middle coding unit 660 b, and the coordinates (xf,yf) that are information indicating a location of the upper-left sample670 c of the right coding unit 660 c. The image decoding apparatus 100may determine the respective sizes of the coding units 660 a, 660 b, and660 c by using the coordinates (xd, yd), (xe, ye), and (xf, yf)indicating the locations of the coding units 660 a, 660 b, and 660 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width of the left coding unit 660 a to be xe-xd. The imagedecoding apparatus 100 may determine the height of the left coding unit660 a to be the height of the current coding unit 650. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe middle coding unit 660 b to be xf-xe. The image decoding apparatus100 may determine the height of the middle coding unit 660 b to be theheight of the current coding unit 650. According to an embodiment, theimage decoding apparatus 100 may determine the width or height of theright coding unit 660 c by using the width or height of the currentcoding unit 650 or the widths or heights of the left and middle codingunits 660 a and 660 b. The image decoding apparatus 100 may determine acoding unit, which has a size different from that of the others, basedon the determined widths and heights of the coding units 660 a, 660 b,and 660 c. Referring to FIG. 6 , the image decoding apparatus 100 maydetermine the middle coding unit 660 b, which has a size different fromthe sizes of the left and right coding units 660 a and 660 c, as thecoding unit of the predetermined location. However, the above-describedmethod, performed by the image decoding apparatus 100, of determining acoding unit having a size different from the size of the other codingunits merely corresponds to an example of determining a coding unit at apredetermined location by using the sizes of coding units, which aredetermined based on coordinates of samples, and thus various methods ofdetermining a coding unit at a predetermined location by comparing thesizes of coding units, which are determined based on coordinates ofpredetermined samples, may be used.

However, locations of samples considered to determine locations ofcoding units are not limited to the above-described upper leftlocations, and information about arbitrary locations of samples includedin the coding units may be used.

According to an embodiment, the image decoding apparatus 100 may selecta coding unit at a predetermined location from among an odd number ofcoding units determined by splitting the current coding unit,considering the shape of the current coding unit. For example, when thecurrent coding unit has a non-square shape, a width of which is longerthan a height, the image decoding apparatus 100 may determine the codingunit at the predetermined location in a horizontal direction. That is,the image decoding apparatus 100 may determine one of coding units atdifferent locations in a horizontal direction and may put a restrictionon the coding unit. When the current coding unit has a non-square shape,a height of which is longer than a width, the image decoding apparatus100 may determine the coding unit at the predetermined location in avertical direction. That is, the image decoding apparatus 100 maydetermine one of coding units at different locations in a verticaldirection and may put a restriction on the coding unit.

According to an embodiment, the image decoding apparatus 100 may useinformation indicating respective locations of an even number of codingunits, to determine the coding unit at the predetermined location fromamong the even number of coding units. The image decoding apparatus 100may determine an even number of coding units by splitting (binarysplitting) the current coding unit, and may determine the coding unit atthe predetermined location by using the information about the locationsof the even number of coding units. An operation related thereto maycorrespond to the operation of determining a coding unit at apredetermined location (e.g., a center location) from among an oddnumber of coding units, which has been described in detail above inrelation to FIG. 6 , and thus detailed descriptions thereof are notprovided here.

According to an embodiment, when a non-square current coding unit issplit into a plurality of coding units, predetermined information abouta coding unit at a predetermined location may be used in a splittingoperation to determine the coding unit at the predetermined locationfrom among the plurality of coding units. For example, the imagedecoding apparatus 100 may use at least one of block shape informationand split shape mode information, which is stored in a sample includedin a middle coding unit, in a splitting operation to determine a codingunit at a center location from among the plurality of coding unitsdetermined by splitting the current coding unit.

Referring to FIG. 6 , the image decoding apparatus 100 may split thecurrent coding unit 600 into the plurality of coding units 620 a, 620 b,and 620 c based on the split shape mode information, and may determinethe coding unit 620 b at a center location from among the plurality ofthe coding units 620 a, 620 b, and 620 c. Furthermore, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation, in consideration of a location from which the split shape modeinformation is obtained. That is, the split shape mode information ofthe current coding unit 600 may be obtained from the sample 640 at acenter location of the current coding unit 600 and, when the currentcoding unit 600 is split into the plurality of coding units 620 a, 620b, and 620 c based on the split shape mode information, the coding unit620 b including the sample 640 may be determined as the coding unit atthe center location. However, information used to determine the codingunit at the center location is not limited to the split shape modeinformation, and various types of information may be used to determinethe coding unit at the center location.

According to an embodiment, predetermined information for identifyingthe coding unit at the predetermined location may be obtained from apredetermined sample included in a coding unit to be determined.Referring to FIG. 6 , the image decoding apparatus 100 may use the splitshape mode information, which is obtained from a sample at apredetermined location in the current coding unit 600 (e.g., a sample ata center location of the current coding unit 600) to determine a codingunit at a predetermined location from among the plurality of the codingunits 620 a, 620 b, and 620 c determined by splitting the current codingunit 600 (e.g., a coding unit at a center location from among aplurality of split coding units). That is, the image decoding apparatus100 may determine the sample at the predetermined location byconsidering a block shape of the current coding unit 600, may determinethe coding unit 620 b including a sample, from which predeterminedinformation (e.g., the split shape mode information) can be obtained,from among the plurality of coding units 620 a, 620 b, and 620 cdetermined by splitting the current coding unit 600, and may put apredetermined restriction on the coding unit 620 b. Referring to FIG. 6, according to an embodiment, the image decoding apparatus 100 maydetermine the sample 640 at the center location of the current codingunit 600 as the sample from which the predetermined information may beobtained, and may put a predetermined restriction on the coding unit 620b including the sample 640, in a decoding operation. However, thelocation of the sample from which the predetermined information can beobtained is not limited to the above-described location, and may includearbitrary locations of samples included in the coding unit 620 b to bedetermined for a restriction.

According to an embodiment, the location of the sample from which thepredetermined information may be obtained may be determined based on theshape of the current coding unit 600. According to an embodiment, theblock shape information may indicate whether the current coding unit hasa square or non-square shape, and the location of the sample from whichthe predetermined information may be obtained may be determined based onthe shape. For example, the image decoding apparatus 100 may determine asample located on a boundary for splitting at least one of a width andheight of the current coding unit in half, as the sample from which thepredetermined information can be obtained, by using at least one ofinformation about the width of the current coding unit and informationabout the height of the current coding unit. As another example, whenthe block shape information of the current coding unit indicates anon-square shape, the image decoding apparatus 100 may determine one ofsamples adjacent to a boundary for splitting a long side of the currentcoding unit in half, as the sample from which the predeterminedinformation can be obtained.

According to an embodiment, when the current coding unit is split into aplurality of coding units, the image decoding apparatus 100 may use thesplit shape mode information to determine a coding unit at apredetermined location from among the plurality of coding units.According to an embodiment, the image decoding apparatus 100 may obtainthe split shape mode information from a sample at a predeterminedlocation in a coding unit, and may split the plurality of coding units,which are generated by splitting the current coding unit, by using thesplit shape mode information, which is obtained from the sample of thepredetermined location in each of the plurality of coding units. Thatis, a coding unit may be recursively split based on the split shape modeinformation, which is obtained from the sample at the predeterminedlocation in each coding unit. An operation of recursively splitting acoding unit has been described above in relation to FIG. 5 , and thusdetailed descriptions thereof will not be provided here.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more coding units by splitting the current coding unit,and may determine an order of decoding the one or more coding units,based on a predetermined block (e.g., the current coding unit).

FIG. 7 illustrates an order of processing a plurality of coding unitswhen an image decoding apparatus determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 710 a and 710 b by splitting a firstcoding unit 700 in a vertical direction, may determine second codingunits 730 a and 730 b by splitting the first coding unit 700 in ahorizontal direction, or may determine second coding units 750 a, 750 b,750 c, and 750 d by splitting the first coding unit 700 in vertical andhorizontal directions, based on split shape mode information.

Referring to FIG. 7 , the image decoding apparatus 100 may determine toprocess the second coding units 710 a and 710 b, which are determined bysplitting the first coding unit 700 in a vertical direction, in ahorizontal direction order 710 c. The image decoding apparatus 100 maydetermine to process the second coding units 730 a and 730 b, which aredetermined by splitting the first coding unit 700 in a horizontaldirection, in a vertical direction order 730 c. The image decodingapparatus 100 may determine the second coding units 750 a, 750 b, 750 c,and 750 d, which are determined by splitting the first coding unit 700in vertical and horizontal directions, according to a predeterminedorder (e.g., a raster scan order or Z-scan order 750 e) by which codingunits in a row are processed and then coding units in a next row areprocessed.

According to an embodiment, the image decoding apparatus 100 mayrecursively split coding units. Referring to FIG. 7 , the image decodingapparatus 100 may determine the plurality of coding units 710 a and 710b, 730 a and 730 b, or 750 a, 750 b, 750 c, and 750 d by splitting thefirst coding unit 700, and may recursively split each of the determinedplurality of coding units 710 a, 710 b, 730 a, 730 b, 750 a, 750 b, 750c, and 750 d. A splitting method of the plurality of coding units 710 aand 710 b, 730 a and 730 b, or 750 a, 750 b, 750 c, and 750 d maycorrespond to a splitting method of the first coding unit 700.Accordingly, each of the plurality of coding units 710 a and 710 b, 730a and 730 b, or 750 a, 750 b, 750 c, and 750 d may be independentlysplit into a plurality of coding units. Referring to FIG. 7 , the imagedecoding apparatus 100 may determine the second coding units 710 a and710 b by splitting the first coding unit 700 in a vertical direction,and may determine to independently split or to not split each of thesecond coding units 710 a and 710 b.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 720 a and 720 b by splitting the leftsecond coding unit 710 a in a horizontal direction, and may not splitthe right second coding unit 710 b.

According to an embodiment, a processing order of coding units may bedetermined based on an operation of splitting a coding unit. In otherwords, a processing order of split coding units may be determined basedon a processing order of coding units immediately before being split.The image decoding apparatus 100 may determine a processing order of thethird coding units 720 a and 720 b determined by splitting the leftsecond coding unit 710 a, independently of the right second coding unit710 b. Because the third coding units 720 a and 720 b are determined bysplitting the left second coding unit 710 a in a horizontal direction,the third coding units 720 a and 720 b may be processed in a verticaldirection order 720 c. Because the left and right second coding units710 a and 710 b are processed in the horizontal direction order 710 c,the right second coding unit 710 b may be processed after the thirdcoding units 720 a and 720 b included in the left second coding unit 710a are processed in the vertical direction order 720 c. An operation ofdetermining a processing order of coding units based on a coding unitbefore being split is not limited to the above-described example, andvarious methods may be used to independently process coding units, whichare split and determined to various shapes, in a predetermined order.

FIG. 8 illustrates a process, performed by an image decoding apparatus,of determining that a current coding unit is to be split into an oddnumber of coding units, when the coding units are not processable in apredetermined order, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine that the current coding unit is split into an odd number ofcoding units, based on obtained split shape mode information. Referringto FIG. 8 , a square first coding unit 800 may be split into non-squaresecond coding units 810 a and 810 b, and the second coding units 810 aand 810 b may be independently split into third coding units 820 a and820 b, and 820 c, 820 d, and 820 e. According to an embodiment, theimage decoding apparatus 100 may determine the plurality of third codingunits 820 a and 820 b by splitting the left second coding unit 810 a ina horizontal direction, and may split the right second coding unit 810 binto the odd number of third coding units 820 c, 820 d, and 820 e.

According to an embodiment, the video decoding apparatus 100 maydetermine whether any coding unit is split into an odd number of codingunits, by determining whether the third coding units 820 a and 820 b,and 820 c, 820 d, and 820 e are processable in a predetermined order.Referring to FIG. 8 , the image decoding apparatus 100 may determine thethird coding units 820 a and 820 b, and 820 c, 820 d, and 820 e byrecursively splitting the first coding unit 800. The image decodingapparatus 100 may determine whether any of the first coding unit 800,the second coding units 810 a and 810 b, or the third coding units 820 aand 820 b, and 820 c, 820 d, and 820 e are split into an odd number ofcoding units, based on at least one of the block shape information andthe split shape mode information. For example, a coding unit located inthe right from among the second coding units 810 a and 810 b may besplit into an odd number of third coding units 820 c, 820 d, and 820 e.A processing order of a plurality of coding units included in the firstcoding unit 800 may be a predetermined order (e.g., a Z-scan order 830),and the image decoding apparatus 100 may determine whether the thirdcoding units 820 c, 820 d, and 820 e, which are determined by splittingthe right second coding unit 810 b into an odd number of coding units,satisfy a condition for processing in the predetermined order.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the third coding units 820 a and 820 b, and 820 c, 820d, and 820 e included in the first coding unit 800 satisfy the conditionfor processing in the predetermined order, and the condition relates towhether at least one of a width and height of the second coding units810 a and 810 b is to be split in half along a boundary of the thirdcoding units 820 a and 820 b, and 820 c, 820 d, and 820 e. For example,the third coding units 820 a and 820 b determined when the height of theleft second coding unit 810 a of the non-square shape is split in halfmay satisfy the condition. It may be determined that the third codingunits 820 c, 820 d, and 820 e do not satisfy the condition because theboundaries of the third coding units 820 c, 820 d, and 820 e determinedwhen the right second coding unit 810 b is split into three coding unitsare unable to split the width or height of the right second coding unit810 b in half. When the condition is not satisfied as described above,the image decoding apparatus 100 may determine disconnection of a scanorder, and may determine that the right second coding unit 810 b is tobe split into an odd number of coding units, based on a result of thedetermination. According to an embodiment, when a coding unit is splitinto an odd number of coding units, the image decoding apparatus 100 mayput a predetermined restriction on a coding unit at a predeterminedlocation from among the split coding units. The restriction or thepredetermined location has been described above in relation to variousembodiments, and thus detailed descriptions thereof will not be providedherein.

FIG. 9 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a first codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may splitthe first coding unit 900, based on split shape mode information, whichis obtained through the receiver 110. The square first coding unit 900may be split into four square coding units, or may be split into aplurality of non-square coding units. For example, referring to FIG. 9 ,when the first coding unit 900 has a square shape and the split shapemode information indicates to split the first coding unit 900 intonon-square coding units, the image decoding apparatus 100 may split thefirst coding unit 900 into a plurality of non-square coding units. Indetail, when the split shape mode information indicates to determine anodd number of coding units by splitting the first coding unit 900 in ahorizontal direction or a vertical direction, the image decodingapparatus 100 may split the square first coding unit 900 into an oddnumber of coding units, e.g., second coding units 910 a, 910 b, and 910c determined by splitting the square first coding unit 900 in a verticaldirection or second coding units 920 a, 920 b, and 920 c determined bysplitting the square first coding unit 900 in a horizontal direction.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the second coding units 910 a, 910 b, 910 c, 920 a,920 b, and 920 c included in the first coding unit 900 satisfy acondition for processing in a predetermined order, and the conditionrelates to whether at least one of a width and height of the firstcoding unit 900 is to be split in half along a boundary of the secondcoding units 910 a, 910 b, 910 c, 920 a, 920 b, and 920 c. Referring toFIG. 9 , because boundaries of the second coding units 910 a, 910 b, and910 c determined by splitting the square first coding unit 900 in avertical direction do not split the width of the first coding unit 900in half, it may be determined that the first coding unit 900 does notsatisfy the condition for processing in the predetermined order. Also,because boundaries of the second coding units 920 a, 920 b, and 920 cdetermined by splitting the square first coding unit 900 in a horizontaldirection do not split the height of the first coding unit 900 in half,it may be determined that the first coding unit 900 does not satisfy thecondition for processing in the predetermined order. When the conditionis not satisfied as described above, the image decoding apparatus 100may decide disconnection of a scan order, and may determine that thefirst coding unit 900 is to be split into an odd number of coding units,based on a result of the decision. According to an embodiment, when acoding unit is split into an odd number of coding units, the imagedecoding apparatus 100 may put a predetermined restriction on a codingunit at a predetermined location from among the split coding units. Therestriction or the predetermined location has been described above inrelation to various embodiments, and thus detailed descriptions thereofwill not be provided herein.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shaped coding units by splitting a first coding unit.

Referring to FIG. 9 , the image decoding apparatus 100 may split thesquare first coding unit 900 or a non-square first coding unit 930 or950 into various-shaped coding units.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined when an image decoding apparatus splits afirst coding unit, satisfies a predetermined condition, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split the square first coding unit 1000 into non-squaresecond coding units 1010 a, and 1010 b or 1020 a and 1020 b, based onsplit shape mode information, which is obtained by the receiver 110. Thesecond coding units 1010 a and 1010 b, or 1020 a and 1020 b may beindependently split. As such, the image decoding apparatus 100 maydetermine to split or to not split each of the second coding units 1010a and 1010 b, or 1020 a and 1020 b into a plurality of coding units,based on the split shape mode information of each of the second codingunits 1010 a and 1010 b, or 1020 a and 1020 b. According to anembodiment, the image decoding apparatus 100 may determine third codingunits 1012 a and 1012 b by splitting the non-square left second codingunit 1010 a, which is determined by splitting the first coding unit 1000in a vertical direction, in a horizontal direction. However, when theleft second coding unit 1010 a is split in a horizontal direction, theimage decoding apparatus 100 may restrict the right second coding unit1010 b to not be split in a horizontal direction in which the leftsecond coding unit 1010 a is split. When third coding units 1014 a and1014 b are determined by splitting the right second coding unit 1010 bin a same direction, because the left and right second coding units 1010a and 1010 b are independently split in a horizontal direction, thethird coding units 1012 a and 1012 b, or 1014 a and 1014 b may bedetermined. However, this case serves equally as a case in which theimage decoding apparatus 100 splits the first coding unit 1000 into foursquare second coding units 1030 a, 1030 b, 1030 c, and 1030 d, based onthe split shape mode information, and may be inefficient in terms ofimage decoding.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 1022 a and 1022 b, or 1024 a and 1024 b bysplitting the non-square second coding unit 1020 a or 1020 b, which isdetermined by splitting the first coding unit 1000 in a horizontaldirection, in a vertical direction. However, when a second coding unit(e.g., the upper second coding unit 1020 a) is split in a verticaldirection, for the above-described reason, the image decoding apparatus100 may restrict the other second coding unit (e.g., the lower secondcoding unit 1020 b) to not be split in a vertical direction in which theupper second coding unit 1020 a is split.

FIG. 11 illustrates a process, performed by an image decoding apparatus,of splitting a square coding unit when split shape mode informationindicates that the square coding unit is to not be split into foursquare coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 1110 a and 1110 b, or 1120 a and 1120 b,etc. by splitting a first coding unit 1100, based on split shape modeinformation. The split shape mode information may include informationabout various methods of splitting a coding unit but, the informationabout various splitting methods may not include information forsplitting a coding unit into four square coding units. According to suchsplit shape mode information, the image decoding apparatus 100 may notsplit the square first coding unit 1100 into four square second codingunits 1130 a, 1130 b, 1130 c, and 1130 d. The image decoding apparatus100 may determine the non-square second coding units 1110 a and 1110 b,or 1120 a and 1120 b, etc., based on the split shape mode information.

According to an embodiment, the image decoding apparatus 100 mayindependently split the non-square second coding units 1110 a and 1110b, or 1120 a and 1120 b, etc. Each of the second coding units 1110 a and1110 b, or 1120 a and 1120 b, etc. may be recursively split in apredetermined order, and this splitting method may correspond to amethod of splitting the first coding unit 1100, based on the split shapemode information.

For example, the image decoding apparatus 100 may determine square thirdcoding units 1112 a and 1112 b by splitting the left second coding unit1110 a in a horizontal direction, and may determine square third codingunits 1114 a and 1114 b by splitting the right second coding unit 1110 bin a horizontal direction. Furthermore, the image decoding apparatus 100may determine square third coding units 1116 a, 1116 b, 1116 c, and 1116d by splitting both of the left and right second coding units 1110 a and1110 b in a horizontal direction. In this case, coding units having thesame shape as the four square second coding units 1130 a, 1130 b, 1130c, and 1130 d split from the first coding unit 1100 may be determined.

As another example, the image decoding apparatus 100 may determinesquare third coding units 1122 a and 1122 b by splitting the uppersecond coding unit 1120 a in a vertical direction, and may determinesquare third coding units 1124 a and 1124 b by splitting the lowersecond coding unit 1120 b in a vertical direction. Furthermore, theimage decoding apparatus 100 may determine square third coding units1126 a, 1126 b, 1126 c, and 1126 d by splitting both the upper and lowersecond coding units 1120 a and 1120 b in a vertical direction. In thiscase, coding units having the same shape as the four square secondcoding units 1130 a, 1130 b, 1130 c, and 1130 d split from the firstcoding unit 1100 may be determined.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may split afirst coding unit 1200, based on split shape mode information. When ablock shape indicates a square shape and the split shape modeinformation indicates to split the first coding unit 1200 in at leastone of horizontal and vertical directions, the image decoding apparatus100 may determine second coding units 1210 a and 1210 b, or 1220 a and1220 b, etc. by splitting the first coding unit 1200. Referring to FIG.12 , the non-square second coding units 1210 a and 1210 b, or 1220 a and1220 b determined by splitting the first coding unit 1200 in only ahorizontal direction or vertical direction may be independently splitbased on the split shape mode information of each coding unit. Forexample, the image decoding apparatus 100 may determine third codingunits 1216 a, 1216 b, 1216 c, and 1216 d by splitting the second codingunits 1210 a and 1210 b, which are generated by splitting the firstcoding unit 1200 in a vertical direction, in a horizontal direction, andmay determine third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b, which are generatedby splitting the first coding unit 1200 in a horizontal direction, in avertical direction. An operation of splitting the second coding units1210 a and 1210 b, or 1220 a and 1220 b has been described above inrelation to FIG. 11 , and thus detailed descriptions thereof will not beprovided herein.

According to an embodiment, the image decoding apparatus 100 may processcoding units in a predetermined order. An operation of processing codingunits in a predetermined order has been described above in relation toFIG. 7 , and thus detailed descriptions thereof will not be providedherein. Referring to FIG. 12 , the image decoding apparatus 100 maydetermine four square third coding units 1216 a, 1216 b, 1216 c, and1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d by splitting the squarefirst coding unit 1200. According to an embodiment, the image decodingapparatus 100 may determine processing orders of the third coding units1216 a, 1216 b, 1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226d based on a split shape by which the first coding unit 1200 is split.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1216 a, 1216 b, 1216 c, and 1216 d bysplitting the second coding units 1210 a and 1210 b generated bysplitting the first coding unit 1200 in a vertical direction, in ahorizontal direction, and may process the third coding units 1216 a,1216 b, 1216 c, and 1216 d in a processing order 1217 for initiallyprocessing the third coding units 1216 a and 1216 c, which are includedin the left second coding unit 1210 a, in a vertical direction and thenprocessing the third coding unit 1216 b and 1216 d, which are includedin the right second coding unit 1210 b, in a vertical direction.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b generated bysplitting the first coding unit 1200 in a horizontal direction, in avertical direction, and may process the third coding units 1226 a, 1226b, 1226 c, and 1226 d in a processing order 1227 for initiallyprocessing the third coding units 1226 a and 1226 b, which are includedin the upper second coding unit 1220 a, in a horizontal direction andthen processing the third coding unit 1226 c and 1226 d, which areincluded in the lower second coding unit 1220 b, in a horizontaldirection.

Referring to FIG. 12 , the square third coding units 1216 a, 1216 b,1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d may bedetermined by splitting the second coding units 1210 a and 1210 b, and1220 a and 1220 b, respectively. Although the second coding units 1210 aand 1210 b are determined by splitting the first coding unit 1200 in avertical direction differently from the second coding units 1220 a and1220 b which are determined by splitting the first coding unit 1200 in ahorizontal direction, the third coding units 1216 a, 1216 b, 1216 c, and1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d split therefromeventually show same-shaped coding units split from the first codingunit 1200. As such, by recursively splitting a coding unit in differentmanners based on the split shape mode information, the image decodingapparatus 100 may process a plurality of coding units in differentorders even when the coding units are eventually determined to be thesame shape.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and a size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine the depth of the coding unit, based on a predeterminedcriterion. For example, the predetermined criterion may be the length ofa long side of the coding unit. When the length of a long side of acoding unit before being split is 2n times (n>0) the length of a longside of a split current coding unit, the image decoding apparatus 100may determine that a depth of the current coding unit is increased froma depth of the coding unit before being split, by n. In the followingdescriptions, a coding unit having an increased depth is expressed as acoding unit of a deeper depth.

Referring to FIG. 13 , according to an embodiment, the image decodingapparatus 100 may determine a second coding unit 1302 and a third codingunit 1304 of deeper depths by splitting a square first coding unit 1300based on block shape information indicating a square shape (e.g., theblock shape information may be expressed as ‘0: SQUARE’). Assuming thatthe size of the square first coding unit 1300 is 2N×2N, the secondcoding unit 1302 determined by splitting a width and height of the firstcoding unit 1300 in ½ may have a size of N×N. Furthermore, the thirdcoding unit 1304 determined by splitting a width and height of thesecond coding unit 1302 in ½ may have a size of N/2×N/2. In this case, awidth and height of the third coding unit 1304 are ¼ times those of thefirst coding unit 1300. When a depth of the first coding unit 1300 is D,a depth of the second coding unit 1302, the width and height of whichare ½ times those of the first coding unit 1300, may be D+1, and a depthof the third coding unit 1304, the width and height of which are ¼ timesthose of the first coding unit 1300, may be D+2.

According to an embodiment, the image decoding apparatus 100 maydetermine a second coding unit 1312 or 1322 and a third coding unit 1314or 1324 of deeper depths by splitting a non-square first coding unit1310 or 1320 based on block shape information indicating a non-squareshape (e.g., the block shape information may be expressed as ‘1: NS_VER’indicating a non-square shape, a height of which is longer than a width,or as ‘2: NS_HOR’ indicating a non-square shape, a width of which islonger than a height).

The image decoding apparatus 100 may determine a second coding unit1302, 1312, or 1322 by splitting at least one of a width and height ofthe first coding unit 1310 having a size of N×2N. That is, the imagedecoding apparatus 100 may determine the second coding unit 1302 havinga size of N×N or the second coding unit 1322 having a size of N×N/2 bysplitting the first coding unit 1310 in a horizontal direction, or maydetermine the second coding unit 1312 having a size of N/2×N bysplitting the first coding unit 1310 in horizontal and verticaldirections.

According to an embodiment, the image decoding apparatus 100 maydetermine the second coding unit 1302, 1312, or 1322 by splitting atleast one of a width and height of the first coding unit 1320 having asize of 2N×N. That is, the image decoding apparatus 100 may determinethe second coding unit 1302 having a size of N×N or the second codingunit 1312 having a size of N/2×N by splitting the first coding unit 1320in a vertical direction, or may determine the second coding unit 1322having a size of N×N/2 by splitting the first coding unit 1320 inhorizontal and vertical directions.

According to an embodiment, the image decoding apparatus 100 maydetermine a third coding unit 1304, 1314, or 1324 by splitting at leastone of a width and height of the second coding unit 1302 having a sizeof N×N. That is, the image decoding apparatus 100 may determine thethird coding unit 1304 having a size of N/2×N/2, the third coding unit1314 having a size of N/4×N/2, or the third coding unit 1324 having asize of N/2×N/4 by splitting the second coding unit 1302 in vertical andhorizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1312 having asize of N/2×N. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1324 having a size of N/2×N/4 by splitting the second coding unit1312 in a horizontal direction, or may determine the third coding unit1314 having a size of N/4×N/2 by splitting the second coding unit 1312in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1322 having asize of N×N/2. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1314 having a size of N/4×N/2 by splitting the second coding unit1322 in a vertical direction, or may determine the third coding unit1324 having a size of N/2×N/4 by splitting the second coding unit 1322in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 may splitthe square coding unit 1300, 1302, or 1304 in a horizontal or verticaldirection. For example, the image decoding apparatus 100 may determinethe first coding unit 1310 having a size of N×2N by splitting the firstcoding unit 1300 having a size of 2N×2N in a vertical direction, or maydetermine the first coding unit 1320 having a size of 2N×N by splittingthe first coding unit 1300 in a horizontal direction. According to anembodiment, when a depth is determined based on the length of thelongest side of a coding unit, a depth of a coding unit determined bysplitting the first coding unit 1300 having a size of 2N×2N in ahorizontal or vertical direction may be the same as the depth of thefirst coding unit 1300.

According to an embodiment, a width and height of the third coding unit1314 or 1324 may be ¼ times those of the first coding unit 1310 or 1320.When a depth of the first coding unit 1310 or 1320 is D, a depth of thesecond coding unit 1312 or 1322, the width and height of which are ½times those of the first coding unit 1310 or 1320, may be D+1, and adepth of the third coding unit 1314 or 1324, the width and height ofwhich are ¼ times those of the first coding unit 1310 or 1320, may beD+2.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shape second coding units by splitting a square firstcoding unit 1400. Referring to FIG. 14 , the image decoding apparatus100 may determine second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d by splitting the first codingunit 1400 in at least one of vertical and horizontal directions based onsplit shape mode information. That is, the image decoding apparatus 100may determine the second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d, based on the split shape modeinformation of the first coding unit 1400.

According to an embodiment, depths of the second coding units 1402 a and1402 b, 1404 a and 1404 b, and 1406 a, 1406 b, 1406 c, and 1406 d thatare determined based on the split shape mode information of the squarefirst coding unit 1400 may be determined based on the length of a longside thereof. For example, because the length of a side of the squarefirst coding unit 1400 equals the length of a long side of thenon-square second coding units 1402 a and 1402 b, and 1404 a and 1404 b,the first coding unit 1400 and the non-square second coding units 1402 aand 1402 b, and 1404 a and 1404 b may have the same depth, e.g., D.However, when the image decoding apparatus 100 splits the first codingunit 1400 into the four square second coding units 1406 a, 1406 b, 1406c, and 1406 d based on the split shape mode information, because thelength of a side of the square second coding units 1406 a, 1406 b, 1406c, and 1406 d is ½ times the length of a side of the first coding unit1400, a depth of the second coding units 1406 a, 1406 b, 1406 c, and1406 d may be D+1 which is deeper than the depth D of the first codingunit 1400 by 1.

According to an embodiment, the image decoding apparatus 100 maydetermine a plurality of second coding units 1412 a and 1412 b, and 1414a, 1414 b, and 1414 c by splitting a first coding unit 1410, a height ofwhich is longer than a width, in a horizontal direction based on thesplit shape mode information. According to an embodiment, the imagedecoding apparatus 100 may determine a plurality of second coding units1422 a and 1422 b, and 1424 a, 1424 b, and 1424 c by splitting a firstcoding unit 1420, a width of which is longer than a height, in avertical direction based on the split shape mode information.

According to an embodiment, a depth of the second coding units 1412 aand 1412 b, and 1414 a, 1414 b, and 1414 c, or 1422 a and 1422 b, and1424 a, 1424 b, and 1424 c, which are determined based on the splitshape mode information of the non-square first coding unit 1410 or 1420,may be determined based on the length of a long side thereof. Forexample, because the length of a side of the square second coding units1412 a and 1412 b is ½ times the length of a long side of the firstcoding unit 1410 having a non-square shape, a height of which is longerthan a width, a depth of the square second coding units 1412 a and 1412b is D+1 which is deeper than the depth D of the non-square first codingunit 1410 by 1.

Furthermore, the image decoding apparatus 100 may split the non-squarefirst coding unit 1410 into an odd number of second coding units 1414 a,1414 b, and 1414 c based on the split shape mode information. The oddnumber of second coding units 1414 a, 1414 b, and 1414 c may include thenon-square second coding units 1414 a and 1414 c and the square secondcoding unit 1414 b. In this case, because the length of a long side ofthe non-square second coding units 1414 a and 1414 c and the length of aside of the square second coding unit 1414 b are ½ times the length of along side of the first coding unit 1410, a depth of the second codingunits 1414 a, 1414 b, and 1414 c may be D+1 which is deeper than thedepth D of the non-square first coding unit 1410 by 1. The imagedecoding apparatus 100 may determine depths of coding units split fromthe first coding unit 1420 having a non-square shape, a width of whichis longer than a height, by using the above-described method ofdetermining depths of coding units split from the first coding unit1410.

According to an embodiment, the image decoding apparatus 100 maydetermine PIDs for identifying split coding units, based on a size ratiobetween the coding units when an odd number of split coding units do nothave equal sizes. Referring to FIG. 14 , a coding unit 1414 b of acenter location among an odd number of split coding units 1414 a, 1414b, and 1414 c may have a width equal to that of the other coding units1414 a and 1414 c and a height which is two times that of the othercoding units 1414 a and 1414 c. That is, in this case, the coding unit1414 b at the center location may include two of the other coding unit1414 a or 1414 c. Therefore, when a PID of the coding unit 1414 b at thecenter location is 1 based on a scan order, a PID of the coding unit1414 c located next to the coding unit 1414 b may be increased by 2 andthus may be 3. That is, discontinuity in PID values may be present.According to an embodiment, the image decoding apparatus 100 maydetermine whether an odd number of split coding units do not have equalsizes, based on whether discontinuity is present in PIDs for identifyingthe split coding units.

According to an embodiment, the image decoding apparatus 100 maydetermine whether to use a specific splitting method, based on PIDvalues for identifying a plurality of coding units determined bysplitting a current coding unit. Referring to FIG. 14 , the imagedecoding apparatus 100 may determine an even number of coding units 1412a and 1412 b or an odd number of coding units 1414 a, 1414 b, and 1414 cby splitting the first coding unit 1410 having a rectangular shape, aheight of which is longer than a width. The image decoding apparatus 100may use PIDs indicating respective coding units so as to identify therespective coding units. According to an embodiment, the PID may beobtained from a sample at a predetermined location of each coding unit(e.g., an upper-left sample).

According to an embodiment, the image decoding apparatus 100 maydetermine a coding unit at a predetermined location from among the splitcoding units, by using the PIDs for distinguishing the coding units.According to an embodiment, when the split shape mode information of thefirst coding unit 1410 having a rectangular shape, a height of which islonger than a width, indicates to split a coding unit into three codingunits, the image decoding apparatus 100 may split the first coding unit1410 into three coding units 1414 a, 1414 b, and 1414 c. The imagedecoding apparatus 100 may assign a PID to each of the three codingunits 1414 a, 1414 b, and 1414 c. The image decoding apparatus 100 maycompare PIDs of an odd number of split coding units to determine acoding unit at a center location from among the coding units. The imagedecoding apparatus 100 may determine the coding unit 1414 b having a PIDcorresponding to a middle value among the PIDs of the coding units, asthe coding unit at the center location from among the coding unitsdetermined by splitting the first coding unit 1410. According to anembodiment, the image decoding apparatus 100 may determine PIDs fordistinguishing split coding units, based on a size ratio between thecoding units when the split coding units do not have equal sizes.Referring to FIG. 14 , the coding unit 1414 b generated by splitting thefirst coding unit 1410 may have a width equal to that of the othercoding units 1414 a and 1414 c and a height which is two times that ofthe other coding units 1414 a and 1414 c. In this case, when the PID ofthe coding unit 1414 b at the center location is 1, the PID of thecoding unit 1414 c located next to the coding unit 1414 b may beincreased by 2 and thus may be 3. When the PID is not uniformlyincreased as described above, the image decoding apparatus 100 maydetermine that a coding unit is split into a plurality of coding unitsincluding a coding unit having a size different from that of the othercoding units. According to an embodiment, when the split shape modeinformation indicates to split a coding unit into an odd number ofcoding units, the image decoding apparatus 100 may split a currentcoding unit in such a manner that a coding unit of a predeterminedlocation among an odd number of coding units (e.g., a coding unit of acenter location) has a size different from that of the other codingunits. In this case, the image decoding apparatus 100 may determine thecoding unit of the center location, which has a different size, by usingPIDs of the coding units. However, the PIDs and the size or location ofthe coding unit of the predetermined location are not limited to theabove-described examples, and various PIDs and various locations andsizes of coding units may be used.

According to an embodiment, the image decoding apparatus 100 may use apredetermined data unit where a coding unit starts to be recursivelysplit.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of predetermined data units included in a picture,according to an embodiment.

According to an embodiment, a predetermined data unit may be defined asa data unit where a coding unit starts to be recursively split by usingsplit shape mode information. That is, the predetermined data unit maycorrespond to a coding unit of an uppermost depth, which is used todetermine a plurality of coding units split from a current picture. Inthe following descriptions, for convenience of explanation, thepredetermined data unit is referred to as a reference data unit.

According to an embodiment, the reference data unit may have apredetermined size and a predetermined shape. According to anembodiment, a reference coding unit may include M×N samples. Herein, Mand N may be equal to each other, and may be integers expressed aspowers of 2. That is, the reference data unit may have a square ornon-square shape, and may be split into an integer number of codingunits.

According to an embodiment, the image decoding apparatus 100 may splitthe current picture into a plurality of reference data units. Accordingto an embodiment, the image decoding apparatus 100 may split theplurality of reference data units, which are split from the currentpicture, by using the split shape mode information of each referencedata unit. The operation of splitting the reference data unit maycorrespond to a splitting operation using a quadtree structure.

According to an embodiment, the image decoding apparatus 100 maypreviously determine the minimum size allowed for the reference dataunits included in the current picture. Accordingly, the image decodingapparatus 100 may determine various reference data units having sizesequal to or greater than the minimum size, and may determine one or morecoding units by using the split shape mode information with reference tothe determined reference data unit.

Referring to FIG. 15 , the image decoding apparatus 100 may use a squarereference coding unit 1500 or a non-square reference coding unit 1502.According to an embodiment, the shape and size of reference coding unitsmay be determined based on various data units capable of including oneor more reference coding units (e.g., sequences, pictures, slices, slicesegments, tiles, tile groups, largest coding units, or the like).

According to an embodiment, the receiver 110 of the image decodingapparatus 100 may obtain, from a bitstream, at least one of referencecoding unit shape information and reference coding unit size informationwith respect to each of the various data units. An operation ofsplitting the square reference coding unit 1500 into one or more codingunits has been described above in relation to the operation of splittingthe current coding unit 300 of FIG. 3 , and an operation of splittingthe non-square reference coding unit 1502 into one or more coding unitshas been described above in relation to the operation of splitting thecurrent coding unit 400 or 450 of FIG. 4 . Thus, detailed descriptionsthereof will not be provided herein.

According to an embodiment, the image decoding apparatus 100 may use aPID for identifying the size and shape of reference coding units, todetermine the size and shape of reference coding units according to somedata units previously determined based on a predetermined condition.That is, the receiver 110 may obtain, from the bitstream, only the PIDfor identifying the size and shape of reference coding units withrespect to each slice, slice segment, tile, tile group, or largestcoding unit which is a data unit satisfying a predetermined condition(e.g., a data unit having a size equal to or smaller than a slice) amongthe various data units (e.g., sequences, pictures, slices, slicesegments, tiles, tile groups, largest coding units, or the like). Theimage decoding apparatus 100 may determine the size and shape ofreference data units with respect to each data unit, which satisfies thepredetermined condition, by using the PID. When the reference codingunit shape information and the reference coding unit size informationare obtained and used from the bitstream according to each data unithaving a relatively small size, efficiency of using the bitstream maynot be high, and therefore, only the PID may be obtained and usedinstead of directly obtaining the reference coding unit shapeinformation and the reference coding unit size information. In thiscase, at least one of the size and shape of reference coding unitscorresponding to the PID for identifying the size and shape of referencecoding units may be previously determined. That is, the image decodingapparatus 100 may determine at least one of the size and shape ofreference coding units included in a data unit serving as a unit forobtaining the PID, by selecting the previously determined at least oneof the size and shape of reference coding units based on the PID.

According to an embodiment, the image decoding apparatus 100 may use oneor more reference coding units included in a largest coding unit. Thatis, a largest coding unit split from a picture may include one or morereference coding units, and coding units may be determined byrecursively splitting each reference coding unit. According to anembodiment, at least one of a width and height of the largest codingunit may be integer times at least one of the width and height of thereference coding units. According to an embodiment, the size ofreference coding units may be obtained by splitting the largest codingunit n times based on a quadtree structure. That is, the image decodingapparatus 100 may determine the reference coding units by splitting thelargest coding unit n times based on a quadtree structure, and may splitthe reference coding unit based on at least one of the block shapeinformation and the split shape mode information according to variousembodiments.

FIG. 16 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture,according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more processing blocks split from a picture. Theprocessing block is a data unit including one or more reference codingunits split from a picture, and the one or more reference coding unitsincluded in the processing block may be determined according to aspecific order. That is, a determination order of one or more referencecoding units determined in each processing block may correspond to oneof various types of orders for determining reference coding units, andmay vary depending on the processing block. The determination order ofreference coding units, which is determined with respect to eachprocessing block, may be one of various orders, e.g., raster scan order,Z-scan, N-scan, up-right diagonal scan, horizontal scan, and verticalscan, but is not limited to the above-mentioned scan orders.

According to an embodiment, the image decoding apparatus 100 may obtainprocessing block size information and may determine the size of one ormore processing blocks included in the picture. The image decodingapparatus 100 may obtain the processing block size information from abitstream and may determine the size of one or more processing blocksincluded in the picture. The size of processing blocks may be apredetermined size of data units, which is indicated by the processingblock size information.

According to an embodiment, the receiver 110 of the image decodingapparatus 100 may obtain the processing block size information from thebitstream according to each specific data unit. For example, theprocessing block size information may be obtained from the bitstream ina data unit such as an image, sequence, picture, slice, slice segment,tile, or tile group. That is, the receiver 110 may obtain the processingblock size information from the bitstream according to each of thevarious data units, and the image decoding apparatus 100 may determinethe size of one or more processing blocks, which are split from thepicture, by using the obtained processing block size information. Thesize of the processing blocks may be integer times that of the referencecoding units.

According to an embodiment, the image decoding apparatus 100 maydetermine the size of processing blocks 1602 and 1612 included in thepicture 1600. For example, the image decoding apparatus 100 maydetermine the size of processing blocks based on the processing blocksize information obtained from the bitstream. Referring to FIG. 16 ,according to an embodiment, the image decoding apparatus 100 maydetermine a width of the processing blocks 1602 and 1612 to be fourtimes the width of the reference coding units, and may determine aheight of the processing blocks 1602 and 1612 to be four times theheight of the reference coding units. The image decoding apparatus 100may determine a determination order of one or more reference codingunits in one or more processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine the processing blocks 1602 and 1612, which are included in thepicture 1600, based on the size of processing blocks, and may determinea determination order of one or more reference coding units in theprocessing blocks 1602 and 1612. According to an embodiment,determination of reference coding units may include determination of thesize of the reference coding units.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, determination order information of one or morereference coding units included in one or more processing blocks, andmay determine a determination order with respect to one or morereference coding units based on the obtained determination orderinformation. The determination order information may be defined as anorder or direction for determining the reference coding units in theprocessing block. That is, the determination order of reference codingunits may be independently determined with respect to each processingblock.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, the determination order information of referencecoding units according to each specific data unit. For example, thereceiver 110 may obtain the determination order information of referencecoding units from the bitstream according to each data unit such as animage, sequence, picture, slice, slice segment, tile, tile group, orprocessing block. Because the determination order information ofreference coding units indicates an order for determining referencecoding units in a processing block, the determination order informationmay be obtained with respect to each specific data unit including aninteger number of processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more reference coding units based on the determineddetermination order.

According to an embodiment, the receiver 110 may obtain thedetermination order information of reference coding units from thebitstream as information related to the processing blocks 1602 and 1612,and the image decoding apparatus 100 may determine a determination orderof one or more reference coding units included in the processing blocks1602 and 1612 and determine one or more reference coding units, whichare included in the picture 1600, based on the determination order.Referring to FIG. 16 , the image decoding apparatus 100 may determinedetermination orders 1604 and 1614 of one or more reference coding unitsin the processing blocks 1602 and 1612, respectively. For example, whenthe determination order information of reference coding units isobtained with respect to each processing block, different types of thedetermination order information of reference coding units may beobtained for the processing blocks 1602 and 1612. When the determinationorder 1604 of reference coding units in the processing block 1602 is araster scan order, reference coding units included in the processingblock 1602 may be determined according to a raster scan order. On thecontrary, when the determination order 1614 of reference coding units inthe other processing block 1612 is a backward raster scan order,reference coding units included in the processing block 1612 may bedetermined according to the backward raster scan order.

According to an embodiment, the image decoding apparatus 100 may decodethe determined one or more reference coding units. The image decodingapparatus 100 may decode an image, based on the reference coding unitsdetermined as described above. A method of decoding the reference codingunits may include various image decoding methods.

According to an embodiment, the image decoding apparatus 100 may obtainblock shape information indicating the shape of a current coding unit orsplit shape mode information indicating a splitting method of thecurrent coding unit, from the bitstream, and may use the obtainedinformation. The split shape mode information may be included in thebitstream related to various data units. For example, the image decodingapparatus 100 may use the split shape mode information included in asequence parameter set, a picture parameter set, a video parameter set,a slice header, a slice segment header, a tile header, or a tile groupheader. Furthermore, the image decoding apparatus 100 may obtain, fromthe bitstream, a syntax element corresponding to the block shapeinformation or the split shape mode information according to eachlargest coding unit, each reference coding unit, or each processingblock, and may use the obtained syntax element.

Hereinafter, a method of determining a split rule, according to anembodiment of the disclosure will be described in detail.

The image decoding apparatus 100 may determine a split rule of an image.The split rule may be predetermined between the image decoding apparatus100 and the image encoding apparatus 2200. The image decoding apparatus100 may determine the split rule of the image, based on informationobtained from a bitstream. The image decoding apparatus 100 maydetermine the split rule based on the information obtained from at leastone of a sequence parameter set, a picture parameter set, a videoparameter set, a slice header, a slice segment header, a tile header,and a tile group header. The image decoding apparatus 100 may determinethe split rule differently according to frames, slices, tiles, temporallayers, largest coding units, or coding units.

The image decoding apparatus 100 may determine the split rule based on ablock shape of a coding unit. The block shape may include a size, shape,a ratio of width and height, and a direction of the coding unit. Theimage encoding apparatus 2200 and the image decoding apparatus 100 maypre-determine to determine the split rule based on the block shape ofthe coding unit. However, the embodiment is not limited thereto. Theimage decoding apparatus 100 may determine the split rule based on theinformation obtained from the bitstream received from the image encodingapparatus 2200.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are the same, theimage decoding apparatus 100 may determine the shape of the coding unitto be a square. Also, when the lengths of the width and height of thecoding unit are not the same, the image decoding apparatus 100 maydetermine the shape of the coding unit to be a non-square.

The size of the coding unit may include various sizes, such as 4×4, 8×4,4×8, 8×8, 16×4, 16×8, and to 256×256. The size of the coding unit may beclassified based on the length of a long side of the coding unit, thelength of a short side, or the area. The image decoding apparatus 100may apply the same split rule to coding units classified as the samegroup. For example, the image decoding apparatus 100 may classify codingunits having the same lengths of the long sides as having the same size.Also, the image decoding apparatus 100 may apply the same split rule tocoding units having the same lengths of long sides.

The ratio of the width and height of the coding unit may include 1:2,2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1, 32:1, 1:32, or the like. Also, adirection of the coding unit may include a horizontal direction and avertical direction. The horizontal direction may indicate a case inwhich the length of the width of the coding unit is longer than thelength of the height thereof. The vertical direction may indicate a casein which the length of the width of the coding unit is shorter than thelength of the height thereof.

The image decoding apparatus 100 may adaptively determine the split rulebased on the size of the coding unit. The image decoding apparatus 100may differently determine an allowable split shape mode based on thesize of the coding unit. For example, the image decoding apparatus 100may determine whether splitting is allowed based on the size of thecoding unit. The image decoding apparatus 100 may determine a splitdirection according to the size of the coding unit. The image decodingapparatus 100 may determine an allowable split type according to thesize of the coding unit.

The split rule determined based on the size of the coding unit may be asplit rule predetermined between the image encoding apparatus 2200 andthe image decoding apparatus 100. Also, the image decoding apparatus 100may determine the split rule based on the information obtained from thebitstream.

The image decoding apparatus 100 may adaptively determine the split rulebased on a location of the coding unit. The image decoding apparatus 100may adaptively determine the split rule based on the location of thecoding unit in the image.

Also, the image decoding apparatus 100 may determine the split rule suchthat coding units generated via different splitting paths do not havethe same block shape. However, an embodiment is not limited thereto, andthe coding units generated via different splitting paths have the sameblock shape. The coding units generated via the different splittingpaths may have different decoding processing orders. Because thedecoding processing orders is described above with reference to FIG. 12, details thereof are not provided again.

Hereinafter, with reference to FIGS. 17 to 20 , video encoding ordecoding method and apparatus will now be described, in which, when amerge candidate list of a current block is configured, it is determinedwhether the number of merge candidates included in the merge candidatelist is greater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, an additional mergecandidate is obtained by using a first merge candidate and a secondmerge candidate of the merge candidate list of the current block, theobtained additional merge candidate is added to the merge candidate listto update the merge candidate list, and prediction is performed on thecurrent block, based on the merge candidate list.

FIG. 17 is a block diagram of a video encoding apparatus according to anembodiment.

A video encoding apparatus 1700 according to an embodiment may include amemory 1710, and at least one processor 1720 connected to the memory1710.

Operations of the video encoding apparatus 1700 according to anembodiment may be performed by individual processors or under a controlby a central processor. Also, the memory 1710 of the video encodingapparatus 1700 may store data received from an external source, and datagenerated by the processor, e.g., information about an additional mergecandidate determined by using a first candidate and a second candidateof a merge candidate list.

When a merge candidate list of a current block is configured, theprocessor 1720 of the video encoding apparatus 1700 may determinewhether the number of merge candidates included in the merge candidatelist is greater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, may obtain an additionalmerge candidate by using a first merge candidate and a second mergecandidate of the merge candidate list of the current block, may add theobatined additional merge candidate to the merge candidate list toupdate the merge candidate list, and may perform prediction on thecurrent block, based on the merge candidate list.

Hereinafter, with reference to FIG. 18 , particular operations of avideo encoding method performed by the video encoding apparatus 1700will now be described, the video encoding method involving, when a mergecandidate list of a current block is configured, determining whether thenumber of merge candidates included in the merge candidate list isgreater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, obtaining an additionalmerge candidate by using a first merge candidate and a second mergecandidate of the merge candidate list of the current block, adding theobtained additional merge candidate to the merge candidate list toupdate the merge candidate list, and performing prediction on thecurrent block, based on the merge candidate list.

FIG. 18 is a flowchart illustrating a video encoding method according toan embodiment.

Referring to FIG. 18 , in operation S1810, when a merge candidate listof a current block is configured, the video encoding apparatus 1700 maydetermine whether the number of merge candidates included in the mergecandidate list is greater than 1 and is smaller than a predeterminedmaximum merge candidate number.

In operation S1830, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, the video encodingapparatus 1700 may obtain an additional merge candidate by using a firstmerge candidate and a second merge candidate of the merge candidate listof the current block.

According to an embodiment, the additional merge candidate may comprisea motion vector having an average value of the first merge candidatemotion vector and the second merge candidate motion vector. In thepresent specification, the additional merge candidate is determined tobe an average of 1 pair of predetermined merge candidates, and thus maybe expressed as a term “pairwise average candidate”.

According to an embodiment, the first merge candidate and the secondmerge candidate may each include at least one of spatial candidatesbeing spatially adjacent to the current block, a temporal candidatebeing temporally adjacent to the current block, and motion vectorcandidates included in a history-based motion vector candidate listincluding a plurality of pieces of motion information of blocks encodedin a merge mode before the current block. A method of configuring themerge candidate list will be described below with reference to FIGS. 21to 23 .

According to an embodiment, the spatial candidates being spatiallyadjacent to the current block may include at least one of a leftadjacent block, an upper adjacent block, a lower-left adjacent block, anupper-right adjacent block, and an upper-left adjacent block whichneighbor the current block.

In operation S1850, the video encoding apparatus 1700 may update themerge candidate list by adding the obtained additional merge candidateto the merge candidate list.

According to an embodiment, after the additional merge candidate isadded to the merge candidate list, when the number of merge candidatesincluded in the merge candidate list is smaller than the predeterminedmaximum merge candidate number, a zero motion vector may be added to themerge candidate list.

In operation S1870, the video encoding apparatus 1700 may performprediction on the current block, based on the merge candidate list.

According to an embodiment, the video encoding apparatus 1700 maydetermine an optimal merge candidate for the current block from amongthe merge candidates of the merge candidate list, and may performprediction on the current block by using the determined optimal mergecandidate. The optimal merge candidate may be determined throughcalculation of a rate-distortion cost with respect to the current block,and information about the optimal merge candidate may be encoded andsignaled.

FIGS. 19 and 20 illustrate a block diagram of a video decoding apparatusaccording to an embodiment and a flowchart of a video decoding methodaccording to an embodiment, respectively corresponding to the videoencoding apparatus and the video encoding method described above.

FIG. 19 illustrates a block diagram of the video decoding apparatusaccording to an embodiment.

A video decoding apparatus 1900 according to an embodiment may include amemory 1910, and at least one processor 1920 connected to the memory1910.

Operations of the video decoding apparatus 1900 according to anembodiment may be performed by individual processors or under a controlby a central processor. Also, the memory 1910 of the video decodingapparatus 1900 may store data received from an external source, and datagenerated by the processor, e.g., information about an additional mergecandidate determined by using a first candidate and a second candidateof a merge candidate list.

When a merge candidate list of a current block is configured, theprocessor 1920 of the video decoding apparatus 1900 may determinewhether the number of merge candidates included in the merge candidatelist is greater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, may obtain an additionalmerge candidate by using a first merge candidate and a second mergecandidate of the merge candidate list of the current block, may add theobtained additional merge candidate to the merge candidate list toupdate the merge candidate list, and may perform prediction on thecurrent block, based on the merge candidate list.

Hereinafter, with reference to FIG. 20 , particular operations of avideo decoding method performed by the video decoding apparatus 1900will now be described, the video decoding method involving, when a mergecandidate list of a current block is configured, determining whether thenumber of merge candidates included in the merge candidate list isgreater than 1 and is smaller than a predetermined maximum mergecandidate number, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, obtaining an additionalmerge candidate by using a first merge candidate and a second mergecandidate of the merge candidate list of the current block, adding theobtained additional merge candidate to the merge candidate list toupdate the merge candidate list, and performing prediction on thecurrent block, based on the merge candidate list.

FIG. 20 illustrates a flowchart of the video decoding method accordingto an embodiment.

Referring to FIG. 20 , in operation S2010, when a merge candidate listof a current block is configured, the video decoding apparatus 1900 maydetermine whether the number of merge candidates included in the mergecandidate list is greater than 1 and is smaller than a predeterminedmaximum merge candidate number.

In operation S2030, when the number of the merge candidates included inthe merge candidate list is greater than 1 and is smaller than thepredetermined maximum merge candidate number, the video decodingapparatus 1900 may obtain an additional merge candidate by using a firstmerge candidate and a second merge candidate of the merge candidate listof the current block.

According to an embodiment, the additional merge candidate may comprisea motion vector having an average value of the first merge candidatemotion vector and the second merge candidate motion vector.

According to an embodiment, the first merge candidate and the secondmerge candidate may each include at least one of spatial candidatesbeing spatially adjacent to the current block, a temporal candidatebeing temporally adjacent to the current block, and motion vectorcandidates included in a history-based motion vector candidate listincluding a plurality of pieces of motion information of blocks encodedin a merge mode before the current block.

According to an embodiment, the spatial candidates being spatiallyadjacent to the current block may include at least one of a leftadjacent block, an upper adjacent block, a lower-left adjacent block, anupper-right adjacent block, and an upper-left adjacent block whichneighbor the current block.

In operation S2050, the video decoding apparatus 1900 may update themerge candidate list by adding the obtained additional merge candidateto the merge candidate list.

According to an embodiment, after the additional merge candidate isadded to the merge candidate list, when the number of merge candidatesincluded in the merge candidate list is smaller than the predeterminedmaximum merge candidate number, a zero motion vector may be added to themerge candidate list.

In operation S2070, the video decoding apparatus 1900 may performprediction on the current block, based on the merge candidate list.

According to an embodiment, the video decoding apparatus 1900 maydetermine an optimal merge candidate for the current block from themerge candidate list, by using information about the optimal mergecandidate, the information being obtained from a bitstream, and mayperform prediction on the current block by using the determined optimalmerge candidate.

FIG. 21 is a diagram for describing a procedure in which a mergecandidate list of a current block is configured.

“Merge mode” refers to a technology of deriving a reference direction, areference picture index, and a motion vector predictor from an adjacentblock of a current block, and in the merge mode, a motion vector valueis calculated by using the motion vector predictor and a motion vectordifference.

Referring to FIG. 21 , to configure the merge candidate list of thecurrent block, a spatial candidate indicating motion information of anadjacent block being spatially adjacent to the current block may befirst scanned, and the scanned spatial candidate may be added to themerge candidate list. For the spatial candidate, positions of 5 blockslocated around the current block may be sequentially scanned. A methodof determining the spatial candidate by scanning the positions of 5blocks will be described below with reference to FIG. 22 .

When configuration of the spatial candidate is completed, configurationof a temporal candidate being temporally adjacent to the current blockis processed. To determine the temporal candidate, a block located at alower-right end of a collocated block of the current block is firstscanned due to prediction performance, and when motion information ofthe block located at the lower-right end does not exist, a block locatedat the center of the collocated block is scanned. The scanned temporalcandidate may be added to the merge candidate list.

When configuration of the temporal candidate is completed, history-basedmotion vector candidates stored in a history-based motion vectorcandidate list may be scanned. In detail, when the number of candidatesstored in the merge candidate list is smaller than a value obtained bysubtracting 1 from a maximum merge candidate number, and the number ofcandidates stored in the history-based motion vector candidate list isgreater than 0, the history-based motion vector candidates stored in thehistory-based motion vector candidate list may be searched. Thehistory-based motion vector candidate list corresponds to a plurality ofpieces of motion information stored as the history-based motion vectorcandidates, the plurality of pieces of motion information being relatedto a block encoded in a merge mode before the current block or a blockreconstructed before the current block. A method of determining a motionvector candidate by using the history-based motion vector candidate listwill be described below with reference to FIG. 23 .

After the merge candidate list is completely configured by using thehistory-based motion vector candidate list, configuration of anadditional merge candidate may be performed. In detail, when the numberof candidates stored in the merge candidate list of the current block issmaller than a predetermined maximum merge candidate number and isgreater than 1, the additional merge candidate may be determined byusing a first candidate and a second candidate stored in the mergecandidate list of the current block. The additional merge candidate maybe an average of the first candidate and the second candidate. Theadditional merge candidate is determined to be an average of 1 pair ofpredetermined merge candidates, and thus may be expressed as a term“pairwise average candidate”.

The first candidate and the second candidate which are used indetermining the pairwise average candidate are stored in the mergecandidate list after scanning of the spatial candidate, the temporalcandidate, and the candidates stored in the history-based motion vectorcandidate list is performed, and thus, each of the first candidate andthe second candidate may be one of the spatial candidate, the temporalcandidate, and the candidates stored in the history-based motion vectorcandidate list.

When the determined pairwise average candidate does not overlap with themerge candidates stored in the merge candidate list, the determinedpairwise average candidate may be added to the merge candidate list, andwhen the determined pairwise average candidate overlaps with the mergecandidates stored in the merge candidate list, the determined pairwiseaverage candidate may not be added to the merge candidate list.

When a type of a slice including the current block indicates auni-direction, the pairwise average candidate is determined to be anaverage of the first candidate and the second candidate. In detail, anaverage of L0 motion vectors of the first candidate and the secondcandidate may be determined to be a L0 motion vector of the currentblock, a L1 reference index of the current block may be set to beunavailable (−1), and L1 prediction of the current block may be set tobe unavailable.

When a type of the slice including the current block indicates abi-direction, it is determined whether prediction of each of the firstcandidate and the second candidate can be derived from a referencepicture list L0 or a reference picture list L1.

In detail, when both the first candidate and the second candidate can bepredicted from the reference picture list L0, a L0 reference index ofthe current block may be set to be a L0 reference index of the firstcandidate, L0 prediction of the current block may be set to beavailable, and the average of L0 motion vectors of the first candidateand the second candidate may be determined to be the L0 motion vector ofthe current block. That is, the average of the L0 motion vectors of thefirst candidate and the second candidate may be determined to be L0pairwise average candidate of the current block.

When both the first candidate and the second candidate can be predictedfrom the reference picture list L1, a L1 reference index of the currentblock may be set to be a L1 reference index of the first candidate, L1prediction of the current block may be set to be available, and anaverage of L1 motion vectors of the first candidate and the secondcandidate may be determined to be L1 motion vector of the current block.That is, the average of the L1 motion vectors of the first candidate andthe second candidate may be determined to be L1 pairwise averagecandidate of the current block.

When the first candidate can be predicted from the reference picturelist L0, and the second candidate cannot be predicted from the referencepicture list L0, the L0 reference index and the L0 motion vector of thecurrent block may be set to be the L0 reference index and the L0 motionvector of the first candidate, and L0 prediction of the current blockmay be set to be available. That is, the L0 motion vector of the firstcandidate may be determined to be L0 pairwise average candidate of thecurrent block.

When the second candidate can be predicted from the reference picturelist L0, and the first candidate cannot be predicted from the referencepicture list L0, the L0 reference index and the L0 motion vector of thecurrent block may be set to be the L0 reference index and the L0 motionvector of the second candidate, and L0 prediction of the current blockmay be set to be available. That is, the L0 motion vector of the secondcandidate may be determined to be L0 pairwise average candidate of thecurrent block.

When the first candidate can be predicted from the reference picturelist L1, and the second candidate cannot be predicted from the referencepicture list L1, the L1 reference index and the L1 motion vector of thecurrent block may be set to be the L1 reference index and the L1 motionvector of the first candidate, and L1 prediction of the current blockmay be set to be available. That is, the L1 motion vector of the firstcandidate may be determined to be L1 pairwise average candidate of thecurrent block.

When the second candidate can be predicted from the reference picturelist L1, and the first candidate cannot be predicted from the referencepicture list L1, the L1 reference index and the L1 motion vector of thecurrent block may be set to be the L1 reference index and the L1 motionvector of the second candidate, and L1 prediction of the current blockmay be set to be available. That is, the L1 motion vector of the secondcandidate may be determined to be L1 pairwise average candidate of thecurrent block.

When both the first candidate and the second candidate cannot bepredicted from the reference picture list L0, the L0 reference index ofthe current block may be set to be unavailable (−1), L0 prediction ofthe current block may be set to be unavailable, and the L0 motion vectorof the current block may be set to be (0, 0). That is, L0 directionprediction of the current block may not be performed.

When both the first candidate and the second candidate cannot bepredicted from the reference picture list L1, the L1 reference index ofthe current block may be set to be unavailable (−1), L1 prediction ofthe current block may be set to be unavailable, and the L1 motion vectorof the current block may be set to be (0, 0). That is, L1 directionprediction of the current block may not be performed.

After pairwise average candidate configuration to the merge candidatelist is completed, when the number of merge candidates included in themerge candidate list is smaller than the predetermined maximum mergecandidate number, a zero motion vector candidate may be added to themerge candidate list.

The aforementioned process of configuring the merge candidate list is nolonger performed when the number of the merge candidates of the mergecandidate list is equal to the predetermined maximum merge candidatenumber.

FIG. 22 is a diagram for describing spatial candidates of a mergecandidate list of a current block.

Referring to FIG. 22 , a scanning process of spatial candidates of acurrent block 2200 is performed in order of an upper adjacent block B1of the current block 2200, a left adjacent block A1 of the current block2200, an upper-right adjacent block B0 of the current block 2200, alower-left adjacent block A0 of the current block 2200, and anupper-left adjacent block B2 of the current block 2200.

According to the order, an adjacent block of the current block 2200 isscanned, whether information of the adjacent block is available isdetermined, the information of the adjacent block is stored as a mergecandidate in a merge candidate list when the information of the adjacentblock is available, and the information of the adjacent block is notstored in the merge candidate list when the information is notavailable. When scanning ends, whether information of an adjacent blockin next order is available is determined, the information of theadjacent block is stored as a merge candidate in the merge candidatelist when the information of the adjacent block is available, and theinformation of the adjacent block is not stored in the merge candidatelist when the information is not available. When scanning of adjacentblocks at 5 positions around the current block is completed, scanning ofa temporal candidate being temporally adjacent to the current block isperformed.

FIG. 23 is a diagram for describing a history-based motion vectorcandidate list of a merge candidate list of a current block.

In history-based motion vector prediction (HMVP), a plurality of piecesof motion information of a previously-encoded block or apreviously-reconstructed block are stored as HMVP candidates. In moredetail, a lookup table storing the HMVP candidates, i.e., a HMVP list,is fetched, and a block is encoded or reconstructed based on the HMVPcandidates of the HMVP list.

Referring to FIG. 23 , an index of a most-recent stored HMVP candidateis 0 and an index of an earliest-stored HMVP candidate is N−1 from amongN HMVP candidates stored in a HMVP lookup table, and according to alookup table sequence order, from HMVP whose index is N−1 to HMVP whoseindex is 0 are scanned.

Also, when the HMVP list is updated and thus a new HMVP candidate isadded thereto, motion information of earliest-stored HMVP0 from amongcandidates stored in the HMVP list may be removed. That is, the HMVPlist is updated according to first-in first-out (FIFO) logic.

According to an embodiment, a plurality of pieces of most-recent storedmotion information may be repetition of motion information equal to aplurality of pieces motion information stored in the general merge list.In this case, a HMVP lookup table usage scheme may be modified, suchthat the plurality of pieces of most-recent stored motion informationmay not be used, and only up to M^(th)-recent stored motion informationmay be used.

FIG. 24A is a diagram for describing pairwise average candidatesaccording to another embodiment, FIG. 24B is a diagram for describing amethod of adding a zero motion vector candidate in a pairwise averagecandidate configuration process according to another embodiment, andFIG. 24C is a diagram for describing a method of adding a half-sizemerge candidate in a pairwise average candidate configuration processaccording to another embodiment.

Referring to FIG. 24A, pairwise average candidates of predeterminedcombinations may be added. In detail, 0, 1, 2, 3 stored inPRIORITY_LIST0 and PRIORITY_LIST1 indicate indices of merge candidatesstored in a merge candidate list, 0 indicates a first candidate storedin the merge candidate list, 1 indicates a second candidate stored inthe merge candidate list, 2 indicates a third candidate stored in themerge candidate list, 3 indicates a fourth candidate stored in the mergecandidate list, 1 to 6 indicating square regions respectively includingpairs of indices refer to an order of combinations of pairwise averagecandidates. For example, according to a first combination scheme of thepairwise average candidates, when a first candidate of 0 inPRIORITY_LIST0 and a second candidate of 1 in PRIORITY_LIST1 areavailable, a pairwise average candidate that is a result of averagingvalues of the two candidates may be added to the merge candidate list.Also, according to a fifth combination scheme of the pairwise averagecandidates, when a second candidate of 1 in PRIORITY_LIST0 and a fourthcandidate of 3 in PRIORITY_LIST1 are available, a pairwise averagecandidate that is a result of averaging values of the two candidates maybe added to the merge candidate list. If possible, computations withrespect to 6 candidates may continue, and results thereof may be addedto the merge candidate list.

In a general merge candidate list, a zero motion vector candidate isadded with a lowest priority to the merge candidate list, but FIG. 24Billustrates a method by which a zero motion vector is added in apairwise average candidate configuration process. Referring to FIG. 24B,a zero motion vector may be inserted into a gap between square regionsrespectively indicating pairs of determining pairwise averagecandidates, and 1 to 5 indicate 5 positions into which a zero motionvectors may be inserted. The zero motion vector may be inserted into atleast one of positions of 1 to 5, and also, a plurality of zero motionvectors may be inserted into the positions of 1 to 5. Efficiency in acase where a zero motion vector candidate is used may be furtherimproved than a case of a pairwise average candidate.

According to another embodiment, a new motion vector candidate may bedetermined by co-averaging a merge candidate and a zero motion vector. Asize of the motion vector candidate is half of a size of an existingcandidate. A motion vector having a half size compared to candidatespre-added to the merge candidate list may also be added to the mergecandidate list. For example, before a pairwise average merge candidateconfiguration process starts, a candidate having a half size compared tothree candidates may be added to the merge candidate list, the threecandidates being stored according to a process of configuring a spatialcandidate and a temporal candidate. Also, a candidate having a half sizecompared to a pairwise average candidate may be added by co-averagingthe pairwise average candidate and a zero motion vector.

Referring to FIG. 24C, a half-size merge candidate may be added in apairwise average candidate configuration process. In FIG. 24C, 1 to 7marked in the front and rear of square regions respectively indicatingpairs of pairwise average candidates refer to positions into which ahalf-size merge candidate may be inserted. In detail, the half-sizemerge candidate may be inserted into at least one of positions of 1 to7, and when a plurality of half-size merge candidates are available, thehalf-size merge candidates may be inserted into a plurality of positionsor may be respectively inserted into positions.

According to another embodiment, in a pairwise average candidateconfiguration process, pairwise average candidates may be configured byusing three pairs by decreasing to first three pairs, not 6 pairs ofFIG. 24A. Also, pairwise average candidates may be configured by usingfirst two pairs. Also, pairwise average candidates may be configured byusing first one pair. Also, pairwise average candidates may beconfigured by using another one pair, e.g., a second candidate and athird candidate, not the first one pair.

Current picture referencing (CPR) or intra block copy (IBC) refers to atechnology of using a current partially-reconstructed frame as onereference picture. In this case, coding units of a current picture mayhave a motion vector indicating its frame. Because use of the currentpicture as a reference picture is differently implemented, compared togeneral inter prediction, when the IBC is applied, i.e., when at leastone reference frame is a current frame, it is not recommended to use apairwise average candidate. Therefore, when the CPR or the IBC isapplied, a pairwise average candidate is not used as a merge candidate.

The disclosure has been particularly shown and described with referenceto embodiments thereof. In this regard, it will be understood by one ofordinary skill in the art that various changes in form and details maybe made therein without departing from the scope of the disclosure.Therefore, the embodiments should be considered in a descriptive senseonly and not for purposes of limitation. The scope of the disclosure isdefined not by the detailed descriptions of the disclosure but by thefollowing claims, and all differences within the scope will be construedas being included in the disclosure.

Meanwhile, the afore-described embodiments of the disclosure can bewritten as a program executable on a computer, and can be implemented ingeneral-use digital computers that execute the program by using acomputer-readable recording medium. Examples of the computer-readablerecording medium include magnetic storage media (e.g., ROM, floppydisks, hard disks, etc.), optical recording media (e.g., CD-ROMs, orDVDs), or the like.

1. A video decoding method comprising: configuring a plurality of mergecandidates for a current block including a first merge candidate and asecond merge candidate; when both the first merge candidate and thesecond merge candidate correspond to a reference picture list L0,determining a motion vector of an additional merge candidate using anaverage value of a first motion vector of the first merge candidate anda second motion vector of the second merge candidate without using anymerge candidate other than the first merge candidate and the secondmerge candidate; and reconstructing the current block using a motionvector of a merge candidate in a merge candidate list including theplurality of merge candidates and the additional merge candidate,wherein the first merge candidate is a merge candidate at a firstposition in the merge candidate list and the second merge candidate is amerge candidate at a second position in the merge candidate list, andwherein the current block has one of a square shape and a non-squareshape.
 2. A video encoding method comprising: configuring a plurality ofmerge candidates for a current block including a first merge candidateand a second merge candidate; when both the first merge candidate andthe second merge candidate correspond to a reference picture list L0,determining a motion vector of an additional merge candidate using anaverage value of a first motion vector of the first merge candidate anda second motion vector of the second merge candidate without using anymerge candidate other than the first merge candidate and the secondmerge candidate; and encoding a residual block indicating a differencebetween an original block of the current block and a prediction block ofthe current block using a motion vector of a merge candidate in a mergecandidate list including the plurality of merge candidates and theadditional merge candidate, wherein the first merge candidate is a mergecandidate at a first position in the merge candidate list and the secondmerge candidate is a merge candidate at a second position in the mergecandidate list, and wherein the current block has one of a square shapeand a non-square shape.
 3. A non-transitory computer-readable medium forrecording a bitstream, the bitstream comprising: a residual blockindicating a difference between an original block of a current block anda prediction block of the current block, wherein, the residual block isobtained by: configuring a plurality of merge candidates for the currentblock including a first merge candidate and a second merge candidate;when both the first merge candidate and the second merge candidatecorrespond to a reference picture list L0, determining a motion vectorof an additional merge candidate using an average value of a firstmotion vector of the first merge candidate and a second motion vector ofthe second merge candidate without using any merge candidate other thanthe first merge candidate and the second merge candidate; and encodingthe residual block using a motion vector of a merge candidate in a mergecandidate list including the plurality of merge candidates and theadditional merge candidate, and wherein the first merge candidate is amerge candidate at a first position in the merge candidate list and thesecond merge candidate is a merge candidate at a second position in themerge candidate list, wherein the current block has one of a squareshape and a non-square shape.